Although my focus is primarily books (I'm the author of 20+ books), I have five screenplays under my belt, several of which are screen adaptations of my novels and four of which have attracted serious producer interest. When I was looking for help with my first screenplay attempt and couldn't find a book or class that presented screenwriting in a way that worked for me, I wrote my own book - Organic Screenwriting: Writing for Film, Naturally. I also teach workshops based on the material in the book.
