Often confused with search engines, directories are completely different.
Unlike search engines, directories use "human indexing;" people review and index links.
Directories have rigid guidelines that sites must meet before being added to their index.
Therefore, they have a smaller, but cleaner index.Yahoo!, LookSmart, MSN, Go and others are directories.
Factors that influence search engine rankings are irrelevant to directory rankings.
Since people review sites, more attention is placed on the quality of a site: its functionality, content and design.
Directories strive to categorize sites accurately and often correct categories suggested by a site's webmaster