Digital marketing became more sophisticated in the 2000s and the 2010s, when[13][14] the proliferation of devices' capable of accessing digital media led to sudden growth.[15] Statistics produced in 2012 and 2013 showed that digital marketing was still growing.[16][17] With the development of social media in the 2000s, such as LinkedIn, Facebook, YouTube and Twitter, consumers became highly dependent on digital electronics in daily lives. Therefore, they expected a seamless user experience across different channels for searching product's information. The change of customer behavior improved the diversification of marketing technology.[18]
Paid search advertising has not been without controversy and the issue of how search engines present advertising on their search result pages has been the target of a series of studies and reports[23][24][25] by Consumer Reports WebWatch. The Federal Trade Commission (FTC) also issued a letter[26] in 2002 about the importance of disclosure of paid advertising on search engines, in response to a complaint from Commercial Alert, a consumer advocacy group with ties to Ralph Nader.
As an Internet marketing strategy, SEO considers how search engines work, the computer programmed algorithms which 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. Optimizing a website may involve editing its content, adding content, doing HTML, and associated coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines. Promoting a site to increase the number of backlinks, or inbound links, is another SEO tactic. By May 2015, mobile search had surpassed desktop search.[3] In 2015, it was reported that Google is developing and promoting mobile search as a key feature within future products. In response, many brands are beginning to take a different approach to their Internet marketing strategies.[4]
"Organic" search engine marketing (organic search listings) combines the best practices of creativity, technology, usability, copy, and online promotion / PR. This is because many search engines base their relevancy algorithms on a combination of the text they see on a page, site, video, or image and combine the content information with external elements such as links and user behaviors/preferences demonstrated over time for a domain, content source, or specific content element.

Search engines use complex mathematical algorithms to guess 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.