Search Engine Optimization techniques are classified into two broad categories: techniques that search engines recommend as part of good design and those techniques that search engines do not approve of and attempt to minimize the effect of, referred to as spamdexing. Some experts classify these methods, and the practitioners who employ them, as either white hat SEO, or black hat SEO. 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.

White SEO conforms to the search engines' guidelines. As the search engine guidelines 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 spiders, rather than attempting to trick the algorithm from its intended purpose. White hat SEO is not exact like website promotion, but they are similar in certain ways.

Black hat SEO attempts to improve rankings in ways that are disapproved of by the search engines, or involve deception. It tries to trick the Search Engine. One black hat technique uses text that is hidden, 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.

Search engines may penalize sites they discover using black hat methods. 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 black hat SEO. Both companies, however, quickly apologized, fixed the offending pages, and were restored to Google's list.