These are my top book recommendations for all composers. I have personally read or used as a reference all of these books and can highly recommend them. Collectively, they have made the biggest impact on my composing.
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Composition and Form

Analyzing Classical Form
by William Caplin
Analyzing Classical Form by William Caplin is will give you a solid toolset for understanding musical form. He bases his theory of form off of many of the ideas from Arnold Schoenberg’s book, The Fundamentals of Musical Composition. I cannot overstate the impact his book has made on my compositional thinking. Highly recommended for all composers.

The Fundamentals of Musical Composition
by Arnold Schoenberg
This books really started me on the right path to understanding composition. Schoenberg has a great way of explaining the processes of composition and breaking them down for beginners.
Books Counterpoint, Partimento, and Solfeggio
In the last decade, there have been many great discoveries about how composition was taught in the past. In particular, there are many interesting aspects around partimento and solfeggio. These books are all great starting points.

Modal Counterpoint: Renaissance Style
by Peter Schubert
This is the best book on modal counterpoint, hands down. He breaks the process into simple steps and has very clear rules to follow. He also gives a great historical perspective by quoting extensively from original manuals on counterpoint from the Renaissance.

The Art of Partimento
by Giorgio Sanguinetti
This is the best book on modal counterpoint, hands down. He breaks the process into simple steps and has very clear rules to follow. He also gives a great historical perspective by quoting extensively from original manuals on counterpoint from the Renaissance.

The Solfeggio Tradition
by Nicholas Baragwanath
This book opened up my mind to new ideas (actually old and lost ideas) about the relationship between singing, melody and counterpoint. It’s a different way to sing solfeggio clarifies key relationships in a more useful way for composing.
Books on Harmony

Voice Leading
by David Huron
Voice Leading by David Huron is a fascinating book that goes into the psychological aspects of how we hear independent musical lines and the principles behind them. For the first time, he has truly cleared up the plethora of conflicting rules given by different books on the subject of voice leading and counterpoint.

A Geometry of Music: Harmony and Counterpoint in the Extended Common Practice
by Dmitri Tymoczko
This is an amazing book that really shows the logic behind how our harmony works. I have referenced his ideas frequently in my courses and articles.

Twentieth-Century Harmony
by Vincent Persichetti
A great resource to break out of traditional harmony.
Books on Orchestration and Notation

Creative Orchestration: A Project Method For Classes In Orchestration And Instrumentation
by George Frederick McKay
Creative Orchestration is one of the few books on orchestration that has actual principles to follow, and not just rules of thumb.

The Study of Orchestration
by Samuel Adler
This is a must read for anyone wanting to learn orchestration.

Textures and Timbres: An Orchestrator’s Handbook
by Henry Brant
For advanced orchestrators, Brant’s book really breaks down balance and timbre like no other author has done before.

Behind Bars: The Definitive Guide To Music Notation
by Elaine Gould
The best resource on music notation. This is always on my desk when I am preparing parts and orchestral scores.