Search engines use complex mathematical algorithms to interpret which websites a user seeks. In this diagram, if each bubble represents a website, programs sometimes called spiders examine which sites link to which other sites, with arrows representing these links. Websites getting more inbound links, or stronger links, are presumed to be more important and what the user is searching for. In this example, since website B is the recipient of numerous inbound links, it ranks more highly in a web search. And the links "carry through", such that website C, even though it only has one inbound link, has an inbound link from a highly popular site (B) while site E does not. Note: Percentages are rounded.

Companies that employ overly aggressive techniques can get their client websites banned from the search results. In 2005, the Wall Street Journal reported on a company, Traffic Power, which allegedly used high-risk techniques and failed to disclose those risks to its clients.[15] Wired magazine reported that the same company sued blogger and SEO Aaron Wall for writing about the ban.[16] Google's Matt Cutts later confirmed that Google did in fact ban Traffic Power and some of its clients.[17]
Optimization techniques are highly tuned to the dominant search engines in the target market. The search engines' market shares vary from market to market, as does competition. In 2003, Danny Sullivan stated that Google represented about 75% of all searches.[64] In markets outside the United States, Google's share is often larger, and Google remains the dominant search engine worldwide as of 2007.[65] As of 2006, Google had an 85–90% market share in Germany.[66] While there were hundreds of SEO firms in the US at that time, there were only about five in Germany.[66] As of June 2008, the market share of Google in the UK was close to 90% according to Hitwise.[67] That market share is achieved in a number of countries.
Google recommends that all websites use https:// when possible. The hostname is where your website is hosted, commonly using the same domain name that you'd use for email. Google differentiates between the "www" and "non-www" version (for example, "" or just ""). When adding your website to Search Console, we recommend adding both http:// and https:// versions, as well as the "www" and "non-www" versions.
Another way search engine marketing is managed is by contextual advertising. Here marketers place ads on other sites or portals that carry information relevant to their products so that the ads jump into the circle of vision of browsers who are seeking information from those sites. A successful SEM plan is the approach to capture the relationships amongst information searchers, businesses, and search engines. Search engines were not important to some industries in the past, but over the past years the use of search engines for accessing information has become vital to increase business opportunities.[31] The use of SEM strategic tools for businesses such as tourism can attract potential consumers to view their products, but it could also pose various challenges.[32] These challenges could be the competition that companies face amongst their industry and other sources of information that could draw the attention of online consumers.[31] To assist the combat of challenges, the main objective for businesses applying SEM is to improve and maintain their ranking as high as possible on SERPs so that they can gain visibility. Therefore, search engines are adjusting and developing algorithms and the shifting criteria by which web pages are ranked sequentially to combat against search engine misuse and spamming, and to supply the most relevant information to searchers.[31] This could enhance the relationship amongst information searchers, businesses, and search engines by understanding the strategies of marketing to attract business.

As the number of sites on the Web increased in the mid-to-late 1990s, search engines started appearing to help people find information quickly. Search engines developed business models to finance their services, such as pay per click programs offered by Open Text[7] in 1996 and then[8] in 1998. later changed its name[9] to Overture in 2001, was purchased by Yahoo! in 2003, and now offers paid search opportunities for advertisers through Yahoo! Search Marketing. Google also began to offer advertisements on search results pages in 2000 through the Google AdWords program. By 2007, pay-per-click programs proved to be primary moneymakers[10] for search engines. In a market dominated by Google, in 2009 Yahoo! and Microsoft announced the intention to forge an alliance. The Yahoo! & Microsoft Search Alliance eventually received approval from regulators in the US and Europe in February 2010.[11]
Snapchat is a popular messaging and picture exchanging application that was created in 2011 by three students at Stanford University named Evan Spiegel, Bobby Murphy, and Reggie Brown. The application was first developed to allow users to message back and forth and to also send photographs that are only available from 1–10 seconds until they are no longer available. The app was an instant hit with social media members and today there are up to 158 million people using snapchat every single day.[60] It is also estimated that Snapchat users are opening the application approximately 18 times per day, which means users are on the app for about 25–30 minutes per day.[60]
Website saturation and popularity, or how much presence a website has on search engines, can be analyzed through the number of pages of the site that are indexed by search engines (saturation) and how many backlinks the site has (popularity). It requires pages to contain keywords people are looking for and ensure that they rank high enough in search engine rankings. Most search engines include some form of link popularity in their ranking algorithms. The following are major tools measuring various aspects of saturation and link popularity: Link Popularity, Top 10 Google Analysis, and Marketleap's Link Popularity and Search Engine Saturation.
Website owners recognized the value of a high ranking and visibility in search engine results,[6] creating an opportunity for both white hat and black hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase "search engine optimization" probably came into use in 1997. Sullivan credits Bruce Clay as one of the first people to popularize the term.[7] On May 2, 2007,[8] Jason Gambert attempted to trademark the term SEO by convincing the Trademark Office in Arizona[9] that SEO is a "process" involving manipulation of keywords and not a "marketing service."