This chapter includes transcriptions and translations of material on keyboard instruments found in the writings of Jakob Adlung, Marin Mersenne, and Michael Praetorius, as well as technical descriptions of the keyboard instruments used by Johann Sebastian Bach, members of the Couperin family, George Frederick Handel, Domenico Scarlatti, Padre Antonio Soler, and other composers of the period. This chapter provides explicit tuning instructions and analysis of temperaments used in the period, notably meantone, temperament ordinaire, and various circulating and so-called “well temperaments” that appear in treatises written by Denis, Corrette, Kirnberger, Mersenne, Marpurg, Neidhardt, Rameau, Werckmeister, and others.