The main purpose of this book is to clarify the meaning and use of the conventions governing the practice of implied accidentals in vocal polyphony from the early fourteenth to the mid-sixteenth century - a problem which has fascinated musicologists for over a hundred years now. Musicians of the late Middle Ages and Renaissance did not think it was necessary to write down all accidentals; since some accidental inflections were implied by the musical context, performers made them whether or not they were notated. This practice imposes on modern readers of early music sources, the task of supplying all such conventionally implied accidental inflections and the successful achievement of this task depends on a knowledge and understanding of the conventions involved. Since the practice of implied accidentals can be understood only in a wider context of compositional, notational, and performing practice of the period, the book attempts to throw light on some aspects of these practices as well.