When search engines first began valuing links as a way to determine the popularity, importance and relevance of a document, they found the classic citation-based rule that what others say about you is far more important (and trustworthy) than what you say about yourself. Thus, while internal links (links that point from one page on your site to another) do carry some weight; links from external sites matter far more.

An obvious one for those in the SEO business, anchor text is one of the biggest factors in the rankings equation overall, so it's no surprise it features prominently in the attributes of a link that engines consider.

In our experiments (and from lots of experience), it appears that "exact match" anchor text is more beneficial than simply inclusion of the target keywords in an anchor text phrase.