These are the selective Internet finding aids that are arranged by subject and include only selected sites. Many portals and search engines have a directory component or partner. Most directories have keyword searching, but entries are also listed under one or more hierarchical subject terms or categories.

A compilation of websites that is categorized and sorted by a topic. Within every directory listing you will find an informative description of each site. When a site is listed on a popular directory, the site has its link popularity. it will increase.

There are two different types of directories, (1) organic and (2) spider built directories. In an organic listing the directories are put together by people who accept or deny the site that has requested placement in the directory. In a spider built directory, a spider (also known as a crawler) follows a URL hyperlinks to certain web pages and puts the relevant hyperlinks into its directory. A web directory or link directory is a directory on the World Wide Web. It specializes in linking to other web sites and categorizing those links.

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 one or two categories. Web directories often allow site owners to directly submit their site for inclusion, and have editors review submissions for fitness.

Some directories are very general in scope and list websites across a wide range of categories, regions and languages. But there are also a large number of 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. A debate over the quality of directories and databases continues, as search engines use ODP's content without real integration, and some experiment using clustering. There have been many attempts to make directory development easier, whether using a "links for all" type link submission site using a script, or any number of available PHP portals and programs. Recently, social software techniques have spawned new efforts of categorization, with Amazon.com adding tagging to their product pages.

• Free Submission - there is no charge for the review and listing of the site
• Reciprocal Link - a link back to the directory must be added somewhere on the submitted site in order to get listed in the directory
• Paid Submissions - a one-time or recurring fee is charged for reviewing/listing the submitted link
• No Follow - there is a rel="nofollow" attribute associated with the link, meaning search engines will not follow the link.
• Featured Listing - the link is given a premium position in a category (or multiple categories) or other sections of the directory, such as the homepage
• Bid for Position - where sites are ordered based on bids
• Affiliate links - where the directory earns commission for referred customers from the listed websites.