Search engine optimization : SEO is the process of growing the quality and quantity of website traffic by increasing the visibility of a website or a web page to users of a web search engine1 SEO refers to the improvement of unpaid results known as natural or organic results and excludes direct traffic and the purchase of paid placement Additionally it may target different kinds of searches including image search video search academic search2 news search and industry-specific vertical search engines Promoting a site to increase the number of back-links or inbound links is another SEO tactic By May 2015 mobile search had surpassed desktop search.

As an Internet marketing strategy SEO considers how search engines work the computer-programmed algorithms that dictate search engine behavior what people search for the actual search terms or keywords typed into search engines and which search engines are preferred by their targeted audience SEO is performed because a website will receive more visitors from a search engine when website ranks are higher in the search engine results page SERP These visitors can then be converted into customers.

SEO differs from local search engine optimization in that the latter is focused on optimizing a business online presence so that its web pages will be displayed by search engines when a user enters a local search for its products or services The former instead is more focused on national or international searches.


Webmasters and content providers began optimizing websites for search engines in the mid1990s as the first search engines were cataloging the early Web Initially all webmasters only needed to submit the address of a page or URL to the various 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 indexed5 The process involves a search engine spider downloading a page and storing it on the search engines own server A second program known as an indexer extracts information about the page such as the words it contains where they are located and any weight for specific words as well as all links the page contains All of this information is then placed into a scheduler for crawling at a later date

Website owners recognized the value of a high ranking and visibility in search engine results6 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 term7 On May 2 20078 Jason Gambert attempted to trademark the term SEO by convincing the Trademark Office in Arizona9 that SEO is a process involving manipulation of keywords and not a marketing service

Early versions of search algorithms relied on webmasterprovided information such as the keyword meta tag or index files in engines like ALIWEB Meta tags provide a guide to each pages content Using metadata to index pages was found to be less than reliable however because the webmasters choice of keywords in the meta tag could potentially be an inaccurate representation of the sites actual content Inaccurate incomplete and inconsistent data in meta tags could and did cause pages to rank for irrelevant searches10dubiousdiscuss Web content providers also manipulated some attributes within the HTML source of a page in an attempt to rank well in search engines11 By 1997 search engine designers recognized that webmasters were making efforts to rank well in their search engine and that some webmasters were even 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

By relying so much on factors such as keyword density which were exclusively within a webmasters 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 stuffed with numerous keywords by unscrupulous webmasters This meant moving away from heavy reliance on term density to a more holistic process for scoring semantic signals13 Since the success and popularity of a search engine is determined by its ability to produce the most relevant results to any given search poor quality or irrelevant search results could lead users to find other search sources Search engines responded by developing more complex ranking algorithms taking into account additional factors that were more difficult for webmasters to manipulate In 2005 an annual conference AIRWeb Adversarial Information Retrieval on the Web was created to bring together practitioners and researchers concerned with search engine optimization and related topics

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 highrisk techniques and failed to disclose those risks to its clients. Wired magazine reported that the same company sued blogger and SEO Aaron Wall for writing about the ban16 Googles Matt Cutts later confirmed that Google did in fact ban Traffic Power and some of its clients.

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 optimization1819 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 website20 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

Relationship with Google

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 links22 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 199823 Google attracted a loyal following among the growing number of Internet users who liked its simple design24 Offpage factors such as PageRank and hyperlink analysis were considered as well as onpage 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 onpage 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 focused on exchanging buying and selling links often on a massive scale Some of these schemes or link farms 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 In June 2007 The New York Times Saul Hansell stated Google ranks sites using more than 200 different signals26 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 opinions27 Patents related to search engines can provide information to better understand search engines28 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 PageRank30 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 wellknown software engineer at Google announced that Google Bot would no longer treat any nofollow links in the same way to prevent SEO service providers from using nofollow for PageRank sculpting31 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 JavaScript32
In December 2009 Google announced it would be using the web search history of all its users in order to populate search results33 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 index34 Google Instant realtimesearch 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 results35
In February 2011 Google announced the Panda update which penalizes websites containing content duplicated from other websites and sources Historically websites have copied content from one another and benefited in search engine rankings by engaging in this practice However Google implemented a new system which punishes sites whose content is not unique36 The 2012 Google Penguin attempted to penalize websites that used manipulative techniques to improve their rankings on the search engine37 Although Google Penguin has been presented as an algorithm aimed at fighting web spam it really focuses on spammy links38 by gauging the quality of the sites the links are coming from The 2013 Google Hummingbird update featured an algorithm change designed to improve Googles natural language processing and semantic understanding of web pages Hummingbirds language processing system falls under the newly recognized term of conversational search where the system pays more attention to each word in the query in order to better match the pages to the meaning of the query rather than a few words39 With regards to the changes made to search engine optimization for content publishers and writers Hummingbird is intended to resolve issues by getting rid of irrelevant content and spam allowing Google to produce highquality content and rely on them to be trusted authors,

In October 2019 Google announced they would start applying BERT models for English language search queries in the US Bidirectional Encoder Representations from Transformers BERT was another attempt by Google to improve their natural language processing but this time in order to better understand the search queries of their users40 In terms of search engine optimization BERT intended to connect users more easily to relevant content and increase the quality of traffic coming to websites that are ranking in the Search Engine Results Page,


Getting indexed

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.

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 review41 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 links42 in addition to their URL submission console43 Yahoo formerly operated a paid submission service that guaranteed crawling for a cost per click44 however this practice was discontinued in 2009
Search engine crawlers may look at a number of different factors when crawling a site Not every page is indexed by the 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,

Today most people are searching on Google using a mobile device46 In November 2016 Google announced a major change to the way crawling websites and started to make their index mobilefirst which means the mobile version of a given website becomes the starting point for what Google includes in their index47 In May 2019 Google updated the rendering engine of their crawler to be the latest version of Chromium 74 at the time of the announcement Google indicated that they would regularly update the Chromium rendering engine to the latest version48 In December 2019 Google began updating the UserAgent 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 UserAgent strings Google ran evaluations and felt confident the impact would be minor.

Preventing crawling

Main article Robots exclusion standard

To avoid undesirable content in the search indexes webmasters can instruct spiders not to crawl certain files or directories through the standard robotstxt file in the root directory of the domain Additionally a page can be explicitly excluded from a search engines database by using a meta tag specific to robots usually meta namerobots contentnoindexWhen a search engine visits a site the robotstxt located in the root directory is the first file crawled The robotstxt file is then parsed and will instruct the robot as to which pages are not to be crawled As a search engine crawler may keep a cached copy of this file it may on occasion crawl pages a webmaster does not wish crawled Pages typically prevented from being crawled include login specific pages such as shopping carts and userspecific content such as search results from internal searches In March 2007 Google warned webmasters that they should prevent indexing of internal search results because those pages are considered search spam.

Increasing prominence

A variety of methods can increase the prominence of a webpage within the search results Cross linking between pages of the same website to provide more links to important pages may improve its visibility51 Writing content that includes frequently searched keyword phrase so as to be relevant to a wide variety of search queries will tend to increase traffic51 Updating content so as to keep search engines crawling back frequently can give additional weight to a site Adding relevant keywords to a web pages metadata including the title tag and meta description will tend to improve the relevancy of a sites search listings thus increasing traffic URL canonicalization of web pages accessible via multiple URLs using the canonical link element52 or via 301 redirects can help make sure links to different versions of the URL all count towards the pages link popularity score.

White hat versus black hat techniques

SEO techniques can be classified into two broad categories techniques that search engine companies recommend as part of good design white hat and those techniques of which search engines do not approve black hat The search engines attempt to minimize the effect of the latter among them spamdexing Industry commentators have classified these methods and the practitioners who employ them as either white hat SEO or black hat SEO53 White hats tend to produce results that last a long time whereas black hats anticipate that their sites may eventually be banned either temporarily or permanently once the search engines discover what they are doing.

An SEO technique is considered white hat if it conforms to the search engines guidelines and involves no deception As the search engine guidelines181955 are not written as a series of rules or commandments this is an important distinction to note White hat SEO is not just about following guidelines but is about ensuring that the content a search engine indexes and subsequently ranks is the same content a user will see White hat advice is generally summed up as creating content for users not for search engines and then making that content easily accessible to the online spider algorithms rather than attempting to trick the algorithm from its intended purpose White hat SEO is in many ways similar to web development that promotes accessibility56 although the two are not identical.

Black hat SEO attempts to improve rankings in ways that are disapproved of by the search engines or involve deception One black hat technique uses hidden text either as text colored similar to the background in an invisible div or positioned off screen Another method gives a different page depending on whether the page is being requested by a human visitor or a search engine a technique known as cloaking Another category sometimes used is grey hat SEO This is in between black hat and white hat approaches where the methods employed avoid the site being penalized but do not act in producing the best content for users Grey hat SEO is entirely focused on improving search engine rankings.

Search engines may penalize sites they discover using black or grey hat methods either by reducing their rankings or eliminating their listings from their databases altogether Such penalties can be applied either automatically by the search engines algorithms or by a manual site review One example was the February 2006 Google removal of both BMW Germany and Ricoh Germany for use of deceptive practices57 Both companies however quickly apologized fixed the offending pages and were restored to Googles search engine results page.

As marketing strategy

SEO is not an appropriate strategy for every website and other Internet marketing strategies can be more effective such as paid advertising through pay per click PPC campaigns depending on the site operators goals Search engine marketing SEM is the practice of designing running and optimizing search engine ad campaigns59 Its difference from SEO is most simply depicted as the difference between paid and unpaid priority ranking in search results Its purpose regards prominence more so than relevance website developers should regard SEM with the utmost importance with consideration to visibility as most navigate to the primary listings of their search60 A successful Internet marketing campaign may also depend upon building high quality web pages to engage and persuade setting up analytics programs to enable site owners to measure results and improving a sites conversion rate61 In November 2015 Google released a full 160 page version of its Search Quality Rating Guidelines to the public62 which revealed a shift in their focus towards usefulness and mobile search In recent years the mobile market has exploded overtaking the use of desktops as shown in by Stat Counter in October 2016 where they analyzed 25 million websites and found that 513 of the pages were loaded by a mobile device63 Google has been one of the companies that are utilizing the popularity of mobile usage by encouraging websites to use their Google Search Console the Mobile Friendly Test which allows companies to measure up their website to the search engine results and how user friendly it is.

SEO may generate an adequate return on investment However search engines are not paid for organic search traffic their algorithms change and there are no guarantees of continued referrals Due to this lack of guarantees and certainty a business that relies heavily on search engine traffic can suffer major losses if the search engines stop sending visitors64 Search engines can change their algorithms impacting a websites placement possibly resulting in a serious loss of traffic According to Googles CEO Eric Schmidt in 2010 Google made over 500 algorithm changesalmost 15 per day65 It is considered a wise business practice for website operators to liberate themselves from dependence on search engine traffic66 In addition to accessibility in terms of web crawlers addressed above user web accessibility has become increasingly important for SEO.

International markets

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 searches67 In markets outside the United States Googles share is often larger and Google remains the dominant search engine worldwide as of 200768 As of 2006 Google had an 8590 market share in Germany69 While there were hundreds of SEO firms in the US at that time there were only about five in Germany69 As of June 2008 the market share of Google in the UK was close to 90 according to Hitwise70 That market share is achieved in a number of countries.

As of 2009 there are only a few large markets where Google is not the leading search engine In most cases when Google is not leading in a given market it is lagging behind a local player The most notable example markets are China Japan South Korea Russia and the Czech Republic where respectively Baidu Yahoo Japan Naver Yandex and Seznam are market leaders.

Successful search optimization for international markets may require professional translation of web pages registration of a domain name with a top level domain in the target market and web hosting that provides a local IP address Otherwise the fundamental elements of search optimization are essentially the same regardless of language.