Richard's Handbook, Playwriting Seminars 2.0, is used by dramatists, screenwriters, novelists, and literary managers in the U.S. and Europe. He is a well known figure in the arts, has led two of the leading university based arts programs in the U.S., and has also worked with Lucasfilm, the BBC, and NPR, in addition to being a judge for screenwriting and playwriting competitions. The Handbook is now available in paperback and e-book editions.
A helpful book that goes into almost everything you'll ever need to write a play and send it off to producers. It can be read all the way through, but much of it is the kind of info you look up on a need to know basis. I'm glad I bought it because it's the kind of book you keep around when questions like, "How wide are a plays margins?" come up.