A search engine, such as Yahoo! or Google, is an online tool that helps users of the World Wide Web find the sites and information they're looking for. Most search engines use automated programs (sometimes called spiders) to look for relevant information based on keywords entered by the user, and search not only web sites' content but also their web addresses, number of pages, and links.

A search directory, such as Yahoo! Directory, is a catalog of web sites organized by category to allow users to easily browse for the information they need. Unlike search engines, which locate and display relevant information based on a defined formula using an automated software program, search directories are organized by real people who discover new sites and relevant information by exploring the Web themselves and reviewing email submissions.

Both search engines and directories can help drive customers to your web site, and neither guarantees that your site will be included.