Online chemical databases are the largest source of chemical information and, therefore, the main resource for retrieving results from published journals, books, patents, conference abstracts, and other relevant sources. Various commercial, as well as free, chemical databases are available. SciFinder, Reaxys, and Web of Science are three major chemical databases that contain extensive search options. Herein, we review these three databases for their search effectiveness and interface. This comparison will be useful to the undergraduates, graduates, nonchemistry majors, researchers, and new librarians.