This book, originally entitled "Gradus ad Parnassum" was the book used by many of the great composers of the classical and romantic eras in learning their craft. Mozart is said to have studied it. Papa Haydn's copy, dog-eared and worn, is on display in a museum in Europe. The book is set up as a series of lessons on the technique of counterpoint, with the student asking questions and the teacher providing answers. There are many examples, both of proper and improper technique. It starts with the easiest forms of counterpoint and moves into the more difficult ones toward the end. It takes itself very seriously and requires a lot of work of the reader. Some of the ideas are outdated, and all of the counterpoint examples are built on bland cantus firmus type melodies, but the exercise of going through this book is invaluable.