In addition to web pages, Google also provides services for searching images, Usenetnewsgroups, news sites, and items for sale online. As of June 2004, Google contained 4.28 billion web pages, 880 million images and 845 million Usenet messages in its index; a total of 6 billion items. It also caches much of the content that it indexes.
The verb "to google" is sometimes used generically to mean "to search the web", although Google itself frowns on this usage as it might lead to their name becoming a genericized trademark.
Convinced that the pages with the most links to them from other highly relevant webpages must be the most relevant ones, Page and Brin decided to test their thesis as part of their studies, and laid the foundation for their search engine. They formally founded their company, Google Inc., on September 7, 1998 in Menlo Park, California in a friend's garage. The company moved to more spacious headquarters in February 1999 in Palo Alto before finally moving to the "Googleplex" later that year.
Google gained a following among Internet users for its simple, clean design and relevant search results. Advertisements were sold by the keyword so that they would be more relevant to the end user, and the ads were text-based in order to keep page design uncluttered and fast-loading. While many of its dot-com siblings went under, Google quietly rose in stature while turning a profit.
In February 2003, Google acquired Pyra Labs, owner of Blogger, a pioneering and leading weblog-hosting website. The acquisition seemed inconsistent with the general mission of Google. However, the move secured the company's ability to utilize information gleaned from blog postings to improve the speed and relevance of articles contained in Google News.
At its peak in early 2004, Google handled upwards of 80% of all search requests on the world wide web through its website and clients like Yahoo, AOL, and CNN.  Google's share fell in February 2004 when Yahoo! dropped Google's search technology in order to deliver independent results.
Google's code of conduct is Don't be evil. Their site includes humorous features such as cartoon modifications of their logo for special occasions, the option to display the site in fictional or humorous languages such as klingon, and April Fool's jokes about the company.
On April 29, 2004, Google filed an S-1 form with the Securities and Exchange Commission for an IPO to raise as much as USD $2,718,281,828 (with a touch of mathematical humor in the exact amount). The filing revealed that Google turned a profit every year since 2001 and earned a profit of $105.6 million on revenues of $961.8 million during 2003.
A number of organizations (most controversially the Church of Scientology) have used the Digital Millennium Copyright Act to demand that Google remove references to allegedly copyrighted material on other sites. Google typically handles this by removing the link as requested and including a link to the complaint in the search results. There have also been complaints that the "Google cache" feature violates copyright. However, the consensus seems to be that caching is a normal part of the functionality of the web, and that HTTP provides adequate mechanisms for requesting that caching be disabled (which Google respects; it also honors the robots.txt file which is a mechanism to allow the owners of a site to request that part or all of their site not be included in search engine listings).
In 2002, news reports surfaced that the Google search engine had been banned in China. A mirror site (in all respects, including mirrored text) called elgooG proved useful to get around the ban. The ban was later lifted, and reports indicated that it was not Google itself that was targeted. Rather, Google's feature of a cached version of a website would allow Chinese users to circumvent any ban of a website itself, merely by visiting the cache instead. There is also a dynamic Google mirror working as a proxy server at http://www.zensur.freerk.com/google/ .
Google's efforts to refine its database has led to some legal controversy, drawing a lawsuit in October 2002 from a company, SearchKing, that sought to sell advertisements on pages with inflated Google rankings. In its defense, Google said that its rankings are its constitutionally protected opinions of the web sites that it lists. A judge threw out SearchKing's lawsuit in mid-2003 on precisely these grounds.
In May 2004, the Baltimore Sun interviewed Peri Fleisher, a great-niece of Edward Kasner, the mathematician whose nephew coined the word "googol", who said Kasner's descendants were "exploring" legal action against Google due to its name. 
Google employs server farms of GNU/Linux computers around the world to answer search requests and to index the web. The server farms are built using a shared nothing architecture. The indexing is performed by a program ("Googlebot") which periodically requests new copies of the web pages it already knows about. The more often a page updates, the more often Googlebot will visit. The links in these pages are examined to discover new pages to be added to its database. The index database and web page cache is several terabytes in size.
The exact size and whereabouts of the physical machines in the google search engine is unknown, and official figures remain intentionally vague. In John Hennessy and David Patterson's Computer Architecture: A Quantitative Approach, the server farmcluster forming the Google "search farm" would in the year 2000 have consisted of about 6000 processors, 12000 common IDE-disks (2 per machine, and one machine per processor), at four sites: two in Silicon Valley and two in Virginia.
Each site had an OC 48 (2488 Mbps, see broadband Internet access article) connection to the Internet and an OC 12 (622 Mbps) connections to other Google sites. The connections are routed through a Cisco 12000 network switch and split by two Foundry Networks BigIron 8000 ethernet switches dividing the traffic onto 4 x 1 Gbps lines connecting up to 64 racks, with 40 machines and an HP Ethernet switch on both back and flip side, so that a rack would fit 80 machines and two HP switches.
Based on the Google IPO S-1 form released in April 2004, Tristan Louis, the Vice President of application development for the Internet unit of a large financial firm, estimated the current server farm to contain something like the following :
253,088 GHz of processing power
126,544 GB of RAM
5,062 TB of hard drive space
According to this estimate, the Google server farm constitutes the most powerful supercomputer in the world, being able to perform at least three times as many calculations per second as the Earth Simulator.
Google uses an algorithm called PageRank to rank web pages that match a given search string. The PageRank algorithm computes a recursive figure of merit for web pages, based on the weighted sum of the PageRanks of the pages linking to them. The PageRank thus derives from human-generated links, and correlates well with human concepts of importance. Previous keyword-based methods of ranking search results, used by many search engines that were once more popular than Google, would rank pages by how often the search terms occurred in the page, or how strongly associated the search terms were within each resulting page. In addition to PageRank, Google also uses other secret criteria for determining the ranking of pages on result lists.
Google not only indexes and caches HTML-files but also 12 other file types, including .PDF, .txt, .doc, and .xls. Except in the case of text files, the cached version is a conversion to HTML. Hence Google allows reading these files even without having the corresponding program such as Word or Excel.
Users can customize the search engine somewhat. They can set a default language, use "SafeSearch" filtering technology, and set the number of results shown on each page. Google has been criticized for placing long-term cookies on users' machines to store these preferences, a tactic which also enables them to track a user's search terms over time. For any query (of which only the 10 first keywords are taken into account), up to the first 1000 results can be shown with a maximum of 100 displayed per page.
Despite its immense index, there is also a considerable amount of data in databases which are accessible from websites by means of queries, but not by links. This so-called deep web is not covered by Google and contains e.g. catalogues of libraries, official legislative documents of governments, phone books, etc.
One technique commonly used is google bombing in which many sites link to another site through a particular word, in order to give the site a high ranking when the word is searched for.
Forums can be found on the web where phenomena such as the "Google dance" are discussed. The Google dance is a period of a few days towards the end of a month when Google updates its database and ranking algorithms. Changes to the database can be observed by examining the number of results to a particular page such as "link:www.yahoo.com".
During the dance period, a site's ranking may change dramatically over a short period of time and different Google servers (e.g., www.google.com, www2.google.com, www3.google.com, www.google.co.uk, www.google.com.au, etc.) may give different results for the same search. The dance period appears to coincide with the time at which the googlebot examines stable sites. Rapidly changing sites, highly ranked sites and news sites are examined more often, although apart from news. Only minor adjustments are made to rankings during most of the month. In some cases it may take two or three months before new pages appear in search results. The monthly searching, indexing and ranking cycle was replaced by a continuous rolling update in the summer of 2003. This change in the way Google updates significantly reduced the unstable results of the monthly update dance.
One of Google's chief challenges is that as its algorithms and results have gained the trust of web users, the profit to be gained by a commercial web site in subverting those results has increased dramatically. Some search engine optimization firms have attempted to inflate specific Google rankings by various artifices, and thereby draw more searchers to their clients' sites. Google has managed to weaken some of these attempts by reducing the ranking of sites Google knows to use them.
Google publishes a set of guidelines  for a website's owners who would like to raise their rankings when using legitimate optimization consultants.
The service covers the news articles that appeared within the past 30 days on news websites in the language concerned, from various countries; for the English language it covers about 4,500 sites, for the other languages less. It provides around the first 200 characters and links to the full article. Some of these websites require a subscription; in that case this is noted in the Google News summary of their articles.
Google News provides searching, and the choice of sorting the results by date and time of publishing (not to be confused with date and time of the news happening) or grouping them (and also grouping without searching). In the English version, there is an option to tailor the grouping to a selected national audience.
Users can request Google News Alerts on various topics by subscribing while using key words. An email is sent when a news article matching the request comes online.
In December 2003, Google announced Froogle, a spin-off that searches catalogues for particular products. This site had been active in beta for some months. It is now offered in Wireless Markup Language (WML) form and can be accessed from phones or other wireless devices that have support for WML.