I wish it were possible to give this book more than five stars.
For precise, copious, detailed information on actors, film makers, and general technical questions this is the place to go. For the most part, this is a biographical dictionary. However, in addition to the 6700 biographies of actors, directors, producers, screenwriters, cameramen, etc., there are also about 1000 articles devoted to technical aspects of film making as well as to short histories of the various national cinemas. Each biographical article also includes, in almost all cases, a complete list of the feature films and shorts to which that individual contributed. Those cases where the list is not complete are usually for actors and film makers from the days of silent films, when accurate and complete recordkeeping was not common. Most silent films, sadly, have been lost anyway.
The articles in this book, in contrast to those in the not recommended "Halliwell's Who's Who in the Movies" (mostly filmographies with little else) are long and detailed. It would be hard to ask for more. I sometimes spend hours pouring over this book.
This is the book that should be on the shelf of every serious cinephile. For quick looks, "Leonard Maltin's Encyclopedia of the Movies" is valuable as well, though it needs to be brought up to date. And for a different point of view on almost everyone associated with film, David Thomson's "New Biographical Dictionary of Film" is a pure delight. (The articles in Thomson's book are mostly critical biographies rather than historical biographies.) But if you must have one book on film, Katz is it.