Search engine optimization
Search engine optimization is the process of improving the quality and quantity of website traffic to a website or a web page from search engines. SEO targets unpaid search traffic rather than direct traffic, referral traffic, social media traffic, or paid traffic.
Organic search engine traffic originates from a variety of searches, including image search, video search, academic search, news search, industry-specific vertical search engines, and large language models.
As an Internet marketing strategy, SEO involves understanding how search engines operate, the algorithms that shape their results, the information users seek, the keywords and queries they enter, and the specific search engines favored by the intended audience. SEO helps websites attract more visitors from a search engine and rank higher within a search engine results page, aiming to either convert the visitors or build brand awareness.
History
s and content providers began optimizing websites for search engines in the mid-1990s as the first search engines were cataloging the early Web. Search engine users would query the URL of a page, and then receive information found on the page, if it existed in the search engine's index.ALIWEB and the earliest versions of search engines required website developers to manually upload website index files in order to be searchable and widely did not utilize any form of ranking algorithm for user queries. The emergence of automated web crawlers would later be used to proactively discover and index websites. This led to website developers to optimize their website’s search signals, including the use of meta tags, to achieve greater visibility in search results.
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.
In some cases, early search algorithms weighted particular HTML attributes in ways that could be leveraged by web content providers to manipulate their search rankings. As early as 1997, search engine providers began adjusting their algorithms to prevent these actions. Eventually, search engines would incorporate more meaningful measures of page purpose, including the more recent development of semantic search.
Some search engines frequently sponsor SEO conferences, webchats, and seminars. Major search engines provide information and guidelines to help with website optimization. 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. 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, resulting in brands and marketers shifting toward mobile-first experiences.
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. This shift has led digital marketers to discuss content formats, authority signals, and how structured data is presented to make content more "promptable".
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."
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. 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. Google attracted a loyal following among the growing number of Internet users, who liked its simple design. Off-page factors were considered as well as on-page factors 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.
By 2004, search engines had incorporated a wide range of undisclosed factors in their ranking algorithms to reduce the impact of link manipulation. 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. Patents related to search engines can provide information to better understand search engines. In 2005, Google began personalizing search results for each user. Depending on their history of previous searches, Google crafted results for logged in users.
In 2007, Google announced a campaign against paid links that transfer PageRank. 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. 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.
In December 2009, Google announced it would be using the web search history of all its users in order to populate search results. 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..." Google Instant, a real-time search feature, was introduced in late 2010 to deliver more timely and relevant results. Historically, site administrators often spent months or years optimizing websites to improve their search rankings. With the rise of social media platforms and blogs, major search engines adjusted their algorithms to enable fresh content to rank more quickly in search results.
Google has implemented numerous algorithm updates to improve search quality, including Panda for content quality, Penguin for link spam, Hummingbird for natural language processing, and BERT for query understanding. These updates reflect the ongoing evolution of search technology and Google's efforts to combat spam while improving user experience.
On May 20, 2025, Google announced that AI Mode would be released to all US users. AI Mode uses what Google calls a "query fan-out technique" which breaks down the search query into multiple sub-topics which generates additional search queries for the user.
Methods
Getting indexed
The leading search engines, such as Google, Bing and Yahoo!, use crawlers to find pages for their algorithmic search results. Pages that are linked from other search engine-indexed pages do not need to be submitted because they are found automatically. The Yahoo! Directory and DMOZ, two major directories which closed in 2014 and 2017 respectively, both required manual submission and human editorial review. Google offers Google Search Console, for which an XML Sitemap feed can be created and submitted for free to ensure that all pages are found, especially pages that are not discoverable by automatically following links in addition to their URL submission console. Yahoo! formerly operated a paid submission service that guaranteed to crawl for a cost per click; however, this practice was discontinued in 2009. Nevertheless, SEO tools such as Semrush enable analysis of both paid and organic traffic by providing insights into cost per click and keyword performance.Search engine crawlers may look at a number of different factors when crawling a site. Not every page is indexed by search engines. The distance of pages from the root directory of a site may also be a factor in whether or not pages get crawled.
Mobile devices are used for the majority of Google searches. In November 2016, Google announced a major change to the way they are crawling websites and started to make their index mobile-first, which means the mobile version of a given website becomes the starting point for what Google includes in their index. In May 2019, Google updated the rendering engine of their crawler to be the latest version of Chromium. Google indicated that they would regularly update the Chromium rendering engine to the latest version. In December 2019, Google began updating the User-Agent string of their crawler to reflect the latest Chrome version used by their rendering service. The delay was to allow webmasters time to update their code that responded to particular bot User-Agent strings. Google ran evaluations and felt confident the impact would be minor.