As a marketing strategy for increasing a site's relevance, SEO considers how search algorithms work and what people search for. SEO efforts may involve a site's coding, presentation, and structure, as well as fixing problems that could prevent search engine indexing programs from fully 'indexing' a site.

Other more noticeable efforts may include adding unique content to a site, ensuring that the content is easily indexed by search engine robots, and making the site more appealing to users.

Pay per click (PPC) is the advertising model used on search engines, advertising networks, and content websites/blogs, where advertisers only pay when a user actually clicks on an advertisement to visit the advertiser's website. 

Advertisers bid on the keywords that they predict their target market will be using as search terms when they are looking for a product or service. When a user types a keyword query matching the advertiser's keyword list, or views a page with relevant content, the advertiser's advertisement may be shown. These 'ads' are called "Sponsored links" or "Sponsored ads" and appear next to or above the "natural" or organic results on search engine results pages, or anywhere a website chooses to on a 'content network' page.

Pay per click ads may also appear on content network websites. In this case, ad networks such as Google AdSense and Yahoo! Publisher Network attempt to provide ads that are relevant to the content of the page where they appear, and no search function is involved.

While many companies exist in this space, Google AdWords, Yahoo! Search Marketing, and Microsoft AdCenter are the largest network operators as of 2007. Minimum prices per click, often referred to as Costs Per Click (CPC), vary depending on the search engine, with some as low at £0.04. Very popular search terms can cost much more on popular engines. Arguably this advertising model may be open to abuse through click fraud, although Google and other search engines have 'supposedly' implemented systems to guard against this.