A WikiProject is a collection of pages devoted to the management of a specific topic or family of topics within Wikipedia; and, simultaneously, a group of editors that use said pages to collaborate on encyclopedic work. It is not a place to write encyclopedia articles directly, but a resource to help coordinate and organize article writing and editing. The attached talk pages are a convenient forum for those interested in a particular project. A WikiProject is a collection of pages devoted to the management of a specific family of information within Wikipedia. ... A WikiProject is a collection of pages devoted to the management of a specific family of information within Wikipedia. ...
Participating
There is a central Directory of WikiProjects available which lists all known projects; for ease of navigation, it has been split into sections by projects topic:
The ChemistryWikiProject is about combining and co-ordinating the many efforts to improve all articles pertaining to chemistry and related subjects, by providing standards and guide where practical.
WikiProjectChemicals, aiming at a full coverage of important chemical compounds.