The linguistic use of pitch is a universal property of spoken language. This book studies one manifestation of this use: grammatical tone, defined as a tone alternation triggered by a grammatical context (not a phonological environment), which functions to express the meaning of that context (for example, adding a high-low melody to a verb in the past tense). The book presents a world-wide survey of this topic, unifying key terminology, establishing important axes of variation, and proposing cross-linguistic principles. While this book is typologically-oriented, it is offered as a resource to both theoretical inquiries as well as descriptive linguistics, and written with both tone specialists and non-specialists in mind.