This is an excellent book for musicians interested in dabbling in composition. It defines the basic terminology frequently used in composition and discusses the common forms: scherzo, theme and variations, rondo, and sonata-allegro. One of the most important things about this book is probably that it does not focus upon the theoretical aspect of music at all. Experience in harmonic structure is not necessary to read this book, although ability to read music is. Most examples are excerpts from common pre-20th century composers such as Bach, Haydn, Mozart, Beethoven, Brahms, etc.
This book is an essential to any musician's library. Even performers can benefit by understanding the forms common in standard repertoire. However, for someone specifically looking for information about harmonic theory, this book provides very little useful information.