A web directory is not a search engine and does not display lists of web pages based on keywords; instead, it lists web sites by category and subcategory. The categorization is usually based on the whole web site rather than one page or a set of keywords, and sites are often limited to inclusion in only a few categories. Web directories often allow site owners to directly submit their site for inclusion, and have editors review submissions for fitness.

Most of the directories are very general in scope and list websites across a wide range of categories, regions and languages. But there are also some niche directories which focus on restricted regions, single languages, or specialist sectors. One type of niche directory with a large number of sites in existence, is the shopping directory for example. Shopping directories specialize in the listing of retail e-commerce sites.

Examples of well known, general, web directories are Yahoo! Directory and the Open Directory Project (ODP). ODP is significant due to its extensive categorization and large number of listings and its free availability for use by other directories and search engines.