Despite the well-known fact that some pieces of Bach's WTC II existed in early forms, there has been no thorough discussion to date as to how the work evolved over the years. Based on an in-depth study of source materials, this book discusses how these sources were produced and how we can use them to evaluate more firmly the origin of the pieces. Tomita and Rastall reveal that the early version of WTCII appear in two distinct phases, reflecting various factors that surrounded the composer's life