A directory is a search tool organized by subject. When searching a directory, start with a general topic and proceed to more specific sub-headings. Professional reviewers select entries in directories, so while there may be fewer sites that are updated less frequently, they are usually valuable.

A search engine is a search tool that uses keywords to compile a list of references or hits. Search engines search larger and more current databases so search terms must be very specific. Because so many references appear it is sometimes hard to find the relevant document for a particular search.

A directory may offer a search option to use both a subject and keyword method. Progressing through the sub-headings, a searcher may switch to keyword searching and will find fewer but more relevant hits. This is a coordinated search method.

A meta-search engine is a search tool that uses keywords to search several search engines at the same time. The engine lists the results by individual search engine or in an integrated single list. This search avoids redundant hits and speeds up the search but may not be as effective for difficult searches.