Tuning the Ear is an ear-training book that develops listening skills through the practice of just intonation, approaching tuning as both a perceptual experience and a concrete musical system grounded in ratio-based harmonic relationships. Through guided exercises, analytical examples, and a clear conceptual framework, the book trains readers to hear beating, resultant tones, and interval color while engaging directly with the practical realities of 7-limit just intonation- including ratio thinking, lattices, harmonic and modal organization. By integrating listening, calculation, and creative application, Tuning the Ear presents just intonation as a living practice in which theory and ear inform one another, offering performers, composers, and curious listeners a practical path toward deeper musical awareness.