Search engine optimization (SEO) is the process of improving the quality and quantity of website traffic to a website or a web page from search engines.[1][2] SEO targets unpaid search traffic (usually referred to as “organic” results) rather than direct traffic, referral traffic, social media traffic, or paid traffic.
Organic search engine traffic originates from a variety of kinds of searches, including image search, video search, academic search,[3] news search, industry-specific vertical search engines, and large language models.
As an Internet marketing strategy, SEO considers how search engines work, the algorithms that dictate search engine results, what people search for, the actual search queries or keywords typed into search engines, and which search engines are preferred by a target audience. SEO helps websites attract more visitors from a search engine and rank higher within a search engine results page (SERP), aiming to either convert the visitors or build brand awareness.[4]
History
Webmasters and content providers began optimizing websites for search engines in the mid-1990s, as the first search engines were cataloging the early Web. Initially, webmasters submitted the address of a page, or URL to the various search engines, which would send a web crawler to crawl that page, extract links to other pages from it, and return information found on the page to be indexed.[5]
According to a 2004 article by former industry analyst and current Google employee Danny Sullivan, the phrase “search engine optimization” came into use in 1997. Sullivan credits SEO practitioner Bruce Clay as one of the first people to popularize the term.[6]
Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag or index files in engines like ALIWEB. Meta tags provide a guide to each page’s content. Using metadata to index pages was found to be less than reliable, however, because the webmaster’s choice of keywords in the meta tag could potentially be an inaccurate representation of the site’s actual content. Flawed data in meta tags, such as those that were inaccurate or incomplete, created the potential for pages to be mischaracterized in irrelevant searches.[7][dubious – discuss]
Web content providers also manipulated attributes within the HTML source of a page in an attempt to rank well in search engines.[8] By 1997, search engine designers recognized that webmasters were making efforts to rank in search engines and that some webmasters were manipulating their rankings in search results by stuffing pages with excessive or irrelevant keywords. Early search engines, such as Altavista and Infoseek, adjusted their algorithms to prevent webmasters from manipulating rankings.[9]
By relying on factors such as keyword density, which were exclusively within a webmaster’s control, early search engines suffered from abuse and ranking manipulation. To provide better results to their users, search engines had to adapt to ensure their results pages showed the most relevant search results, rather than unrelated pages with numerous keywords by unscrupulous webmasters. This meant moving away from heavy reliance on term density to a more holistic process for scoring semantic signals.[10]
Search engines responded by developing more complex ranking algorithms, taking into account additional factors that were more difficult for webmasters to manipulate.[citation needed]
Some search engines have also reached out to the SEO industry and are frequent sponsors and guests at SEO conferences, webchats, and seminars. Major search engines provide information and guidelines to help with website optimization.[11][12] Google has a Sitemaps program to help webmasters learn if Google is having any problems indexing their website and also provides data on Google traffic to the website.[13] Bing Webmaster Tools provides a way for webmasters to submit a sitemap and web feeds, allows users to determine the “crawl rate”, and track the web pages index status.
In 2015, it was reported that Google was developing and promoting mobile search as a key feature within future products. In response, many brands began to take a different approach to their Internet marketing strategies.[14]
In the 2020s, the rise of generative AI tools such as ChatGPT, Claude, Perplexity, and Gemini gave rise to discussion around a concept variously referred to as generative engine optimization, answer engine optimization or artificial intelligence optimization. This approach focuses on optimizing content for inclusion in AI-generated answers provided by large language models (LLMs). This shift has led digital marketers to discuss content formats, authority signals, and how structured data is presented to make content more “promptable”.[15] It has also been argued that each of these tactics should be considered as subsets of “search experience optimization,” described by Ahrefs as “optimizing a brand’s presence for non-linear search journeys over multiple platforms, not just Google.”[16]
Relationship between Google and SEO industry
In 1998, two graduate students at Stanford University, Larry Page and Sergey Brin, developed “Backrub”, a search engine that relied on a mathematical algorithm to rate the prominence of web pages. The number calculated by the algorithm, PageRank, is a function of the quantity and strength of inbound links.[17] PageRank estimates the likelihood that a given page will be reached by a web user who randomly surfs the web and follows links from one page to another. In effect, this means that some links are stronger than others, as a higher PageRank page is more likely to be reached by the random web surfer.
Page and Brin founded Google in 1998.[18] Google attracted a loyal following among the growing number of Internet users, who liked its simple design.[19] Off-page factors (such as PageRank and hyperlink analysis) were considered as well as on-page factors (such as keyword frequency, meta tags, headings, links and site structure) to enable Google to avoid the kind of manipulation seen in search engines that only considered on-page factors for their rankings. Although PageRank was more difficult to game, webmasters had already developed link-building tools and schemes to influence the Inktomi search engine, and these methods proved similarly applicable to gaming PageRank. Many sites focus on exchanging, buying, and selling links, often on a massive scale. Some of these schemes involved the creation of thousands of sites for the sole purpose of link spamming.[20]
By 2004, search engines had incorporated a wide range of undisclosed factors in their ranking algorithms to reduce the impact of link manipulation.[21] The leading search engines, Google, Bing, and Yahoo, do not disclose the algorithms they use to rank pages. Some SEO practitioners have studied different approaches to search engine optimization and have shared their personal opinions.[22] Patents related to search engines can provide information to better understand search engines.[23] In 2005, Google began personalizing search results for each user. Depending on their history of previous searches, Google crafted results for logged in users.[24]
In 2007, Google announced a campaign against paid links that transfer PageRank.[25] On June 15, 2009, Google disclosed that they had taken measures to mitigate the effects of PageRank sculpting by use of the nofollow attribute on links. Matt Cutts, a well-known software engineer at Google, announced that Google Bot would no longer treat any no follow links, in the same way, to prevent SEO service providers from using nofollow for PageRank sculpting.[26] As a result of this change, the usage of nofollow led to evaporation of PageRank. In order to avoid the above, SEO engineers developed alternative techniques that replace nofollowed tags with obfuscated JavaScript and thus permit PageRank sculpting. Additionally, several solutions have been suggested that include the usage of iframes, Flash, and JavaScript.[27]
In December 2009, Google announced it would be using the web search history of all its users in order to populate search results.[28] On June 8, 2010 a new web indexing system called Google Caffeine was announced. Designed to allow users to find news results, forum posts, and other content much sooner after publishing than before, Google Caffeine was a change to the way Google updated its index in order to make things show up quicker on Google than before. According to Carrie Grimes, the software engineer who announced Caffeine for Google, “Caffeine provides 50 percent fresher results for web searches than our last index…”[29] Google Instant, real-time-search, was introduced in late 2010 in an attempt to make search results more timely and relevant. Historically site administrators have spent months or even years optimizing a website to increase search rankings. With the growth in popularity of social media sites and blogs, the leading engines made changes to their algorithms to allow fresh content to rank quickly within the search results.[30]
Google has implemented numerous algorithm updates to improve search quality, including Panda (2011) for content quality, Penguin (2012) for link spam, Hummingbird (2013) for natural language processing, and BERT (2019) for query understanding. These updates reflect the ongoing evolution of search technology and Google’s efforts to combat spam while improving user experience.