This collection brings together an anthology of articles by Thomas Christensen, one of the leading historians of music theory active today. Published over the span of the past 25 years, the selected articles provide a historical conspectus about a range of vital topics in the history of music theory, focusing in particular upon writings from the seventeenth and eighteenth centuries. Christensen examines a variety of theorists and their arguments within the intellectual and musical contexts of their time, in the process highlighting the diverse and idiosyncratic nature of the discipline of music theory itself. In the first section of the book Christensen offers general reflections on the meaning and interpretation of historical music theories, with especial attention paid to their value for music theorists today. The second section of the book contains a number of articles that consider the catalytic role of the thorough bass in the development of harmonic theory during the seventeenth and eighteenth centuries. In the final two sections of the anthology, focus turns to the writings of several individual music theorists, including Marin Mersenne, Seth Calvisius, Johann Mattheson, Johann Nicolaus Bach, Denis Diderot and Johann Nichelmann. The volume includes essays from hard-to-find publications as well as newly-translated material and the articles are prefaced by a new, wide-ranging autobiographical essay by the author that offers a broad re-assessment of his historical project. This book is essential reading for music theorists and seventeenth- and eighteenth-century musicologists.