Google Algorithm Change History

Each year, Google changes its search algorithm up to 500 – 600 times. While most of these changes are minor, every few months Google rolls out a “major” algorithmic update that affect search results in significant ways.
For search marketers, knowing the dates of these Google updates can help explain changes in rankings and organic website traffic. Below, we’ve listed the major algorithmic changes that made the biggest impacts on search. Understanding these updates can help with search engine optimization.

2012 Updates

DMCA Penalty — August 10, 2012

Google announced that they would start penalizing sites with repeat copyright violations, probably via DMCA takedown requests. Timing was stated as "starting next week" (8/13?).
An update to our search algorithms (Google)
The Emanuel Update: Google Will Penalize Sites Repeatedly Accused Of Copyright Infringement (SEL)

June/July 86-Pack — August 10, 2012

After a summer hiatus, the June and July Search Quality Highlights were rolled out in one mega-post. Major updates included Panda data and algorithm refreshes, an improved rank-ordering function (?), a ranking boost for "trusted sources", and changes to site clustering.
Search quality highlights: 86 changes for June and July (Google)
Google’s June-July Updates: Site Clustering, Sitelinks Changes & Focus On Page Quality (SEL) 

Panda 3.9 — July 24, 2012

A month after Panda 3.8, Google rolled out a new Panda update. Rankings fluctuated for 5-6 days, although no single day was high enough to stand out. Google claimed ~1% of queries were impacted.
Official: Google Panda 3.9 Refresh (SER)

Link Warnings — July 19, 2012

In a repeat of March/April, Google sent out a large number of unnatural link warnings via Google Webmaster Tools. In a complete turn-around, they then announced that these new warnings may not actually represent a serious problem.
Insanity: Google Sends New Link Warnings, Then Says You Can Ignore Them (SEL)
Google Sends Out New Batch Of Unnatural Link Notifications (SER)

Panda 3.8 — June 25, 2012

Google rolled out another Panda data refresh, but this appeared to be data only (no algorithm changes) and had a much smaller impact than Panda 3.7.
Official Google Panda Update Version 3.8 On June 25th (SEL)
Google Panda 3.8 Live: June 25th & Refresh Only (SER)

Panda 3.7 — June 8, 2012

Google rolled out yet another Panda data update, claiming that less than 1% of queries were affect. Ranking fluctuation data suggested that the impact was substantially higher than previous Panda updates (3.5, 3.6).
Confirmed: Google Panda 3.7 Update (SER)
The Bigfoot Update (AKA Dr. Pete Goes Crazy) (SEOmoz)

May 39-Pack — June 7, 2012

Google released their monthly Search Highlights, with 39 updates in May. Major changes included Penguin improvements, better link-scheme detection, changes to title/snippet rewriting, and updates to Google News.
Search quality highlights: 39 changes for May (Google)
Google’s May Updates: Inorganic Backlinks, Page Titles, Fresh Results & More (SEL)

Penguin 1.1 — May 25, 2012

Google rolled out its first targeted data update after the "Penguin" algorithm update. This confirmed that Penguin data was being processed outside of the main search index, much like Panda data.
Google Releases Penguin Update 1.1 (SEL)

Knowledge Graph — May 16, 2012

In a major step toward semantic search, Google started rolling out "Knowledge Graph", a SERP-integrated display providing supplemental object about certain people, places, and things. Expect to see "knowledge panels" appear on more and more SERPs over time. Also, Danny Sullivan's favorite Trek is ST:Voyager?!
Introducing the Knowledge Graph: things, not strings (Google)
Google Launches Knowledge Graph To Provide Answers, Not Just Links (SEL)

April 52-Pack — May 4, 2012

Google published details of 52 updates in April, including changes that were tied to the "Penguin" update. Other highlights included a 15% larger "base" index, improved pagination handling, and a number of updates to sitelinks.
Search quality highlights: 52 changes for April (Google)
Google’s April Updates: Bigger & Tiered Index, Document Ranking, Sitelink Changes & More (SEL)

Panda 3.6 — April 27, 2012

Barely a week after Panda 3.5, Google rolled out yet another Panda data update. The implications of this update were unclear, and it seemed that the impact was relatively small.
Confirmed: Panda Update 3.6 Happened On April 27th (SEL)

Penguin — April 24, 2012

After weeks of speculation about an "Over-optimization penalty", Google finally rolled out the "Webspam Update", which was soon after dubbed "Penguin." Penguin adjusted a number of spam factors, including keyword stuffing, and impacted an estimated 3.1% of English queries.
Another step to reward high-quality sites (Google)
The Penguin Update: Google’s Webspam Algorithm Gets Official Name (SEL)
Google Penguin Update Recovery Tips & Advice (SEL)
Two Weeks In, Google Talks Penguin Update, Ways To Recover & Negative SEO (SEL)

Panda 3.5 — April 19, 2012

In the middle of a busy week for the algortihm, Google quietly rolled out a Panda data update. A mix of changes made the impact difficult to measure, but this appears to have been a fairly routine update with minimal impact.
Google Mocks Me For Missing Panda 3.5 (SER)

Parked Domain Bug — April 16, 2012

After a number of webmasters reported ranking shuffles, Google confirmed that a data error had caused some domains to be mistakenly treated as parked domains (and thereby devalued). This was not an intentional algorithm change.
Dropped In Rankings? Google’s Mistake Over Parked Domains Might Be To Blame (SEL)
Updated: Google Update April 2012? Over SEO Penalty? (SER)

March 50-Pack — April 3, 2012

Google posted another batch of update highlights, covering 50 changes in March. These included confirmation of Panda 3.4, changes to anchor-text "scoring", updates to image search, and changes to how queries with local intent are interpreted.
Search quality highlights: 50 changes for March (Google)
Google’s March Updates: Anchor Text, Image Search, Navigational Search & More (SEL)

Panda 3.4 — March 23, 2012

Google announced another Panda update, this time via Twitter as the update was rolling out. Their public statements estimated that Panda 3.4 impacted about 1.6% of search results.
Google Says Panda 3.4 Is ‘Rolling Out Now’ (SEL)

Search Quality Video — March 12, 2012

This wasn't an algorithm update, but Google published a rare peek into a search quality meeting. For anyone interested in the algorithm, the video provides a lot of context to both Google's process and their priorities. It's also a chance to see Amit Singhal in action.
Video! The search quality meeting, uncut (Google)

Panda 3.3 — February 27, 2012

Google rolled out another post-"flux" Panda update, which appeared to be relatively minor. This came just 3 days after the 1-year anniversary of Panda, an unprecedented lifespan for a named update.
Google Confirms Panda 3.3 Update (SEL)
Confirmed: Google Panda 3.3 (SER)

February 40-Pack (2) — February 27, 2012

Google published a second set of "search quality highlights" at the end of the month, claiming more than 40 changes in February. Notable changes included multiple image-search updates, multiple freshness updates (including phasing out 2 old bits of the algorithm), and a Panda update.
Search quality highlights: 40 changes for February (Google)

Venice — February 27, 2012

As part of their monthly update, Google mentioned code-name "Venice". This local update appeared to more aggressively localize organic results and more tightly integrate local search data. The exact roll-out date was unclear.
Understand and Rock the Google Venice Update (SEOmoz)
Google Venice Update – New Ranking Opportunities for Local SEO (Catalyst eMarketing)

February 17-Pack — February 3, 2012

Google released another round of "search quality highlights" (17 in all). Many related to speed, freshness, and spell-checking, but one major announcement was tighter integration of Panda into the main search index.
17 search quality highlights: January (Google)
Google’s January Search Update: Panda In The Pipelines, Fresher Results, Date Detection & More (SEL)

Ads Above The Fold — January 19, 2012

Google updated their page layout algorithms to devalue sites with too much ad-space above the "fold". It was previously suspected that a similar factor was in play in Panda. The update had no official name, although it was referenced as "Top Heavy" by some SEOs.
Page layout algorithm improvement (Google)
Pages With Too Many Ads “Above The Fold” Now Penalized By Google’s “Page Layout” Algorithm (SEL)

Panda 3.2 — January 18, 2012

Google confirmed a Panda data update, although suggested that the algorithm hadn't changed. It was unclear how this fit into the "Panda Flux" scheme of more frequent data updates.
Confirmed: Google Panda 3.2 Update (SEW)
Google Panda 3.2 Update Confirmed (SEL)

Search + Your World — January 10, 2012

Google announced a radical shift in personalization - aggressively pushing Google+ social data and user profiles into SERPs. Google also added a new, prominent toggle button to shut off personalization.
Search, plus Your World (Google)
Real-Life Examples Of How Google’s “Search Plus” Pushes Google+ Over Relevancy (SEL)

January 30-Pack — January 5, 2012

Google announced 30 changes over the previous month, including image search landing-page quality detection, more relevant site-links, more rich snippets, and related-query improvements. The line between an "algo update" and a "feature" got a bit more blurred.
30 search quality highlights - with codenames! (Google)
Google Announces “Megasitelinks,” Image Search Improvements & Better Byline Dates (SEL)

2011 Updates

December 10-Pack — December 1, 2011

Google outlined a second set of 10 updates, announcing that these posts would come every month. Updates included related query refinements, parked domain detection, blog search freshness, and image search freshness. The exact dates of each update were not provided.
Search quality highlights: new monthly series on algorithm changes (Google)
Google: Parked Domains, Scraper Sites Targeted Among New Search Changes (SEL)

Panda 3.1 — November 18, 2011

After Panda 2.5, Google entered a period of "Panda Flux" where updates started to happen more frequently and were relatively minor. Some industry analysts called the 11/18 update 3.1, even though there was no official 3.0. For the purposes of this history, we will discontinue numbering Panda updates except for very high-impact changes.
Google Panda 3.1 Update: 11/18 (SER)

10-Pack of Updates — November 14, 2011

This one was a bit unusual. In a bid to be more transparent, Matt Cutts released a post with 10 recent algorithm updates. It's not clear what the timeline was, and most were small updates, but it did signal a shift in how Google communicates algorithm changes.
Ten recent algorithm changes (Google)
Improved Snippets, Rank Boost For “Official” Pages Among 10 New Google Algorithm Changes (SEL)

Freshness Update — November 3, 2011

Google announced that an algorithm change rewarding freshness would impact up to 35% of queries (almost 3X the publicly stated impact of Panda 1.0). This update primarly affected time-sensitive results, but signalled a much stronger focus on recent content.
Giving you fresher, more recent search results (Google)
Google Search Algorithm Change For Freshness To Impact 35% Of Searches (SEL)

Query Encryption — October 18, 2011

Google announced they would be encrypting search queries, for privacy reasons. Unfortunately, this disrupted organic keyword referral data, returning "(not provided)" for some organic traffic. This number increased in the weeks following the launch.
Making search more secure (Google)
Google Hides Search Referral Data with New SSL Implementation (SEOmoz)

Panda "Flux" — October 5, 2011

Matt Cutts tweeted: "expect some Panda-related flux in the next few weeks" and gave a figure of "~2%". Other minor Panda updates occurred on 10/3, 10/13, and 11/18.
Taking a Closer Look at the Google’s Panda 2.5 “Flux” (SEL)
“Minor” Google Panda Update On November 18th (SEL)

Panda 2.5 — September 28, 2011

After more than month, Google rolled out another Panda update. Specific details of what changed were unclear, but some sites reported large-scale losses.
Confirmed: Google Panda 2.5 Update Arrived This Week (SEL)
Google Panda 2.5: Losers Include Today Show, The Next Web; Winners Include YouTube, Fox News (SEL)

516 Algo Updates — September 21, 2011

This wasn't an update, but it was an amazing revelation. Google CEO Eric Schmidt told Congress that Google made 516 updates in 2010. The real shocker? They tested over 13,000 updates.
Eric Schmidt's Congressional Testimony (SEL)

Pagination Elements — September 15, 2011

To help fix crawl and duplication problems created by pagination, Google introduced the rel="next" and rel="prev" link attributes. Google also announced that they had improved automatic consolidation and canonicalization for "View All" pages.
Pagination with rel=“next” and rel=“prev” (Google)
Google Provides New Options for Paginated Content (SEL)

Expanded Sitelinks — August 16, 2011

After experimenting for a while, Google officially rolled out expanded site-links, most often for brand queries. At first, these were 12-packs, but Google appeared to limit the expanded site-links to 6 shortly after the roll-out.
The evolution of sitelinks: expanded and improved (Google)
Official: Google Sitelinks Expands To 12 Pack (SEL)

Panda Goes Global (2.4) — August 12, 2011

Google rolled Panda out internationally, both for English-language queries globally and non-English queries except for Chinese, Japanese, and Korean. Google reported that this impacted 6-9% of queries in affected countries.
High-quality sites algorithm launched in additional languages (Google)
Google’s Panda Update Launches Internationally in Most Languages (SEL)

Panda 2.3 — July 23, 2011

Webmaster chatter suggested that Google rolled out yet another update. It was unclear whether new factors were introduced, or this was simply an update to the Panda data and ranking factors.
Official: Google Panda 2.3 Update Is Live (SEL)
A Holistic Look at Panda with Vanessa Fox (Stone Temple)

Google+ — June 28, 2011

After a number of social media failures, Google launched a serious attack on Facebook with Google+. Google+ revolved around circles for sharing content, and was tightly integrated into products like Gmail. Early adopters were quick to jump on board, and within 2 weeks Google+ reached 10M users.
Introducing the Google+ project: Real-life sharing, rethought for the web (Google)
Larry Page On Google+: Over 10 Million Users, 1 Billion Items Being Shared Per Day (TechCrunch)

Panda 2.2 — June 21, 2011

Google continued to update Panda-impacted sites and data, and version 2.2 was officially acknowledged. Panda updates occurred separately from the main index and not in real-time, reminiscent of early Google Dance updates.
Official: Google Panda Update 2.2 Is Live (SEL)
Why Google Panda Is More A Ranking Factor Than Algorithm Update (SEL)

Schema.org — June 2, 2011

Google, Yahoo and Microsoft jointly announced support for a consolidated approach to structured data. They also created a number of new "schemas", in an apparent bid to move toward even richer search results.
Google, Bing & Yahoo Unite To Make Search Listings Richer Through Structured Data (SEL) What is Schema.org? (Schema.org)

Panda 2.1 — May 9, 2011

Initially dubbed “Panda 3.0”, Google appeared to roll out yet another round of changes. These changes weren’t discussed in detail by Google and seemed to be relatively minor.
It’s Panda Update 2.1, Not Panda 3.0, Google Says (SEL)
Google Panda 3.0 (SERoundtable)

Panda 2.0 — April 11, 2011

Google rolled out the Panda update to all English queries worldwide (not limited to English-speaking countries). New signals were also integrated, including data about sites users blocked via the SERPs directly or the Chrome browser.
High-quality sites algorithm goes global, incorporates user feedback (Google)
Panda 2.0: Google Rolls Out Panda Update Internationally & Incorporates Searcher Blocking Data (SEL)

The +1 Button — March 30, 2011

Responding to competition by major social sites, including Facebook and Twitter, Google launched the +1 button (directly next to results links). Clicking [+1] allowed users to influence search results within their social circle, across both organic and paid results.
Recommendations when you want them (Google)
Meet +1: Google's Answer To The Facebook Like Button (SEL)

Panda/Farmer — February 23, 2011

A major algorithm update hit sites hard, affecting up to 12% of search results (a number that came directly from Google). Panda seemed to crack down on thin content, content farms, sites with high ad-to-content ratios, and a number of other quality issues. Panda rolled out over at least a couple of months, hitting Europe in April 2011.
The 'Panda' That Hates Farms: A Q&A With Google's Top Search Engineers (Wired)
Google's Farmer/Panda Update: Analysis of Winners vs. Losers (SEOmoz)

Attribution Update — January 28, 2011

In response to high-profile spam cases, Google rolled out an update to help better sort out content attribution and stop scrapers. According to Matt Cutts, this affected about 2% of queries. It was a clear precursor to the Panda updates.
Algorithm Change Launched (Matt Cutts)
Latest Google Algorithm change (Search News Central)

Overstock.com Penalty — January 2011

In a rare turn of events, a public outing of shady SEO practices by Overstock.com resulted in a very public Google penalty. JCPenney was hit with a penalty in February for similar bad behavior. Both situations represented a shift in Google's attitude and foreshadowed the Panda update.
Google Penalizes Overstock for Search Tactics (WSJ)
Overstock.com's Google Rankings - Too Good? (WMW)

2010 Updates

Social Signals — December 2010

Google and Bing confirmed that they use social signals in determining ranking, including data from Twitter and Facebook. Matt Cutts confirmed that this was a relatively new development for Google, although many SEOs had long suspected it would happen.
What Social Signals Do Google & Bing Really Count? (SEL)
Google Webmaster Video Reconfirms Use Of Social Signals (SEL)

Negative Reviews — December 2010

After an expose in the New York Times about how e-commerce site DecorMyEyes was ranking based on negative reviews, Google made a rare move and reactively adjusted the algorithm to target sites using similar tactics.
A Bully Finds a Pulpit on the Web (NY Times)
Being bad to your customers is bad for business (Google)

Instant Previews — November 2010

A magnifying glass icon appeared on Google search results, allowing search visitors to quickly view a preview of landing pages directly from SERPs. This signaled a renewed focus for Google on landing page quality, design, and usability.
Beyond Instant Results: Instant Previews (Google)

Google Instant — September 2010

Expanding on Google Suggest, Google Instant launched, displaying search results as a query was being typed. SEOs everywhere nearly spontaneously combusted, only to realize that the impact was ultimately fairly small.
About Google Instant (Google)
Google Instant: Fewer Changes to SEO than the Average Algo Update (SEOmoz)

Brand Update — August 2010

Although not a traditional algorithm update, Google started allowing the same domain to appear multiple times on a SERP. Previously, domains were limited to 1-2 listings, or 1 listing with indented results.
Google Search Results Dominated By One Domain (SEL)

Caffeine (Rollout) — June 2010

After months of testing, Google finished rolling out the Caffeine infrastructure. Caffeine not only boosted Google's raw speed, but integrated crawling and indexation much more tightly, resulting in (according to Google) a 50% fresher index.
Our new search index: Caffeine (Google)
Google’s New Indexing Infrastructure “Caffeine” Now Live (SEL)

May Day — May 2010

In late April and early May, webmasters noticed significant drops in their long-tail traffic. Matt Cutts later confirmed that May Day was an algorithm change impacting the long-tail. Sites with large-scale thin content seemed to be hit especially hard, foreshadowing the Panda update.
Google Search Results Dominated By One Domain (SEL)
Video: Google's Matt Cutts On May Day Update (SERoundtable)

Google Places — April 2010

Although "Places" pages were rolled out in September of 2009, they were originally only a part of Google Maps. The official launch of Google Places re-branded the Local Business Center, integrated Places pages more closely with local search results, and added a number of features, including new local advertising options.
Google Local Business Center Becomes "Google Places" (SEL)
Introducing Google Places (Google)

2009 Updates

Real-time Search — December 2009

This time, real-time search was for real- Twitter feeds, Google News, newly indexed content, and a number of other sources were integrated into a real-time feed on some SERPs. Sources continued to expand over time, including social media.
Google Launches Real Time Search Results (SEL)

Caffeine (Preview) — August 2009

Google released a preview of a massive infrastructure change, designed to speed crawling, expand the index, and integrate indexation and ranking in nearly real-time. The timeline spanned months, with the final rollout starting in the US in early 2010 and lasting until the summer.
Google Caffeine: A Detailed Test of the New Google (Mashable)
Help test some next-generation infrastructure (Google)

Rel-canonical Tag — February 2009

Google, Microsoft, and Yahoo jointly announced support for the Canonical Tag, allowing webmasters to send canonicalization signals to search bots without impacting human visitors.
Learn about the Canonical Link Element in 5 minutes (MattCutts.com)
Canonical URL Tag - The Most Important Advancement in SEO Practices Since Sitemaps (SEOmoz)

Vince — February 2009

SEOs reported a major update that seemed to strongly favor big brands. Matt Cutts called Vince a "minor change", but others felt it had profound, long-term implications.
Big Brands - Google Brand Promotion: New Search Engine Rankings Place Heavy Emphasis on Branding (SEO Book)
Google's Vince Update Produces Big Brand Rankings; Google Calls It A Trust "Change" (SEL)

2008 Updates

Google Suggest — August 2008

In a major change to their logo-and-a-box home-page Google introduced Suggest, displaying suggested searches in a dropdown below the search box as visitors typed their queries. Suggest would later go on to power Google Instant.
Google.com Finally Gets Google Suggest Feature (SEL)

Dewey — April 2008

A large-scale shuffle seemed to occur at the end of March and into early April, but the specifics were unclear. Some suspected Google was pushing its own internal properties, including Google Books, but the evidence of that was limited.
Google's Cutts Asking for Feedback on March/April '08 Update (SERoundtable)

2007 Updates

Buffy — June 2007

In honor of Vanessa Fox leaving Google, the "Buffy" update was christened. No one was quite sure what happened, and Matt Cutts suggested that Buffy was just an accumulation of smaller changes.
Google "Buffy" Update - June Google.com Update (SERoundtable)
SMX Seattle wrap-up (MattCutts.com)

Universal Search — May 2007

While not your typical algorithm update, Google integrated traditional search results with News, Video, Images, Local, and other verticals, dramatically changing their format. The old 10-listing SERP was officially dead. Long live the old 10-listing SERP.
Google 2.0: Google Universal Search (SEL)

2006 Updates

False Alarm — December 2006

There were stirrings about an update in December, along with some reports of major ranking changes in November, but Google reported no major changes.
Google Update Debunked By Matt Cutts (SERoundtable)

Supplemental Update — November 2006

Throughout 2006, Google seemed to make changes to the supplemental index and how filtered pages were treated. They claimed in late 2006 that supplemental was not a penalty (even if it sometimes felt that way).
Confusion Over Google's Supplemental Index (SERoundtable)

2005 Updates

Big Daddy — December 2005

Technically, Big Daddy was an infrastructure update (like the more recent "Caffeine"), and it rolled out over a few months, wrapping up in March of 2006. Big Daddy changed the way Google handled URL canonicalization, redirects (301/302) and other technical issues.
Indexing timeline (MattCutts.com)
Todd, Greg & Matt Cutts on WebMasterRadio (SEOmoz)

Jagger — October 2005

Google released a series of updates, mostly targeted at low-quality links, including reciprocal links, link farms, and paid links. Jagger rolled out in at least 3 stages, from roughly September to November of 2005, with the greatest impact occurring in October.
A Review Of The Jagger 2 Update (SERoundtable)
Dealing With Consequences of Jagger Update (WMW)

Google Local/Maps — October 2005

After launching the Local Business Center in March 2005 and encouraging businesses to update their information, Google merged its Maps data into the LBC, in a move that would eventually drive a number of changes in local SEO.
Google Merges Local and Maps Products (Google)

Gilligan — September 2005

Also called the "False" update ? webmasters saw changes (probably ongoing), but Google claimed no major algorithm update occurred. Matt Cutts wrote a blog post explaining that Google updated (at the time) index data daily but Toolbar PR and some other metrics only once every 3 months.
Google's Cutts Says Not An Update - I Say An Update, Just Not A Dance (SEW)
What?s an update? (MattCutts.com)

Personalized Search — June 2005

Unlike previous attempts at personalization, which required custom settings and profiles, the 2005 roll-out of personalized search tapped directly into users? search histories to automatically adjust results. Although the impact was small at first, Google would go on to use search history for many applications.
Google Relaunches Personal Search - This Time, It Really Is Personal (SEW)
Search gets personal (Google)

XML Sitemaps — June 2005

Google allowed webmasters to submit XML sitemaps via Webmaster Tools, bypassing traditional HTML sitemaps, and giving SEOs direct (albeit minor) influence over crawling and indexation.
New "Google Sitemaps" Web Page Feed Program (SEW)

Bourbon — May 2005

"GoogleGuy" (likely Matt Cutts) announced that Google was rolling out "something like 3.5 changes in search quality." No one was sure what 0.5 of a change was, but Webmaster World members speculated that Bourbon changed how duplicate content and non-canonical (www vs. non-www) URLs were treated.
Google Update "Bourbon" (Batelle Media)
Bourbon Update Survival Kit (SERoundtable)

Allegra — February 2005

Webmasters witnessed ranking changes, but the specifics of the update were unclear. Some thought Allegra affected the "sandbox" while others believed that LSI had been tweaked. Additionally, some speculated that Google was beginning to penalize suspicious links.
Google's Feb. 2005 Update (SEW)

Nofollow — January 2005

To combat spam and control outbound link quality, Google, Yahoo, and Microsoft collectively introduce the "nofollow" attribute. Nofollow helps clean up unvouched for links, including spammy blog comments. While not a traditional algorithm update, this change gradually has a significant impact on the link graph.
Google, Yahoo, MSN Unite On Support For Nofollow Attribute For Links (SEW)

2004 Updates

Google IPO — August 2004

Although obviously not an algorithm update, a major event in Google's history - Google sold 19M shares, raised $1.67B in capital, and set their market value at over $20B. By January 2005, Google share prices more than doubled.
Google IPO priced at $85 a share (CNN)

Brandy — February 2004

Google rolled out a variety of changes, including a massive index expansion, Latent Semantic Indexing (LSI), increased attention to anchor text relevance, and the concept of link "neighborhoods." LSI expanded Google's ability to understand synonyms and took keyword analysis to the next level.
Google's Brandy Update Exposed (WebProNews)
How To Beat Google's "Brandy" Update (SitePoint)

Austin — January 2004

What Florida missed, Austin came in to clean up. Google continued to crack-down on deceptive on-page tactics, including invisible text and META-tag stuffing. Some speculated that Google put the "Hilltop" algorithm into play and began to take page relevance seriously.
The latest on update Austin (Google's January update) (SEJ)
Google Update Austin: Google Update Florida Again (Search-Marketing.info)

2003 Updates

Florida — November 2003

This was the update that put updates (and probably the SEO industry) on the map. Many sites lost ranking, and business owners were furious. Florida sounded the death knell for low-value late 90s SEO tactics, like keyword stuffing, and made the game a whole lot more interesting.
What Happened To My Site On Google? (SEW)

Supplemental Index — September 2003

In order to index more documents without sacrificing performance, Google split off some results into the "supplemental" index. The perils of having results go supplemental became a hotly debated SEO topic, until the index was later reintegrated.
Search Engine Size Wars & Google's Supplemental Results (SEW)

Fritz — July 2003

The monthly "Google Dance" finally came to an end with the "Fritz" update. Instead of completely overhauling the index on a roughly monthly basis, Google switched to an incremental approach. The index was now changing daily.
Explaining algorithm updates and data refreshes (Matt Cutts)
Exclusive: How Google’s Algorithm Rules the Web (Wired) 

Esmerelda — June 2003

This marked the last of the regular monthly Google updates, as a more continuous update process began to emerge. The "Google Dance" was replaced with "Everflux". Esmerelda probably heralded some major infrastructure changes at Google.
Google Update Esmeralda (Kuro5hin)

Dominic — May 2003

While many changes were observed in May, the exact nature of Dominic was unclear. Google bots "Freshbot" and "Deepcrawler" scoured the web, and many sites reported bounces. The way Google counted or reported backlinks seemed to change dramatically.
Understanding Dominic - Part 2 (WMW)

Cassandra — April 2003

Google cracked down on some basic link-quality issues, such as massive linking from co-owned domains. Cassandra also came down hard on hidden text and hidden links.
Google - Update "Cassandra" is here (Econsultancy)

Boston — February 2003

Announced at SES Boston, this was the first named Google update. Originally, Google aimed at a major monthly update, so the first few updates were a combination of algorithm changes and major index refreshes (the so-called "Google Dance"). As updates became more frequent, the monthly idea quickly died.

2002 Updates

1st Documented Update — September 2002

Before "Boston" (the first named update), there was a major shuffle in the Fall of 2002. The details are unclear, but this appeared to be more than the monthly Google Dance and PageRank update. As one webmaster said of Google: "they move the toilet mid stream".
September, 2002 Google Update Discussion - Part 1 (WMW)
Dancing The Google Dance (Level343)

2000 Updates

Google Toolbar — December 2000

Guaranteeing SEO arguments for years to come, Google launched their browser toolbar, and with it, Toolbar PageRank (TBPR). As soon as webmasters started watching TBPR, the Google Dance began.
Google Launches The Google Toolbar (Google)

Source: SEOMOZ