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 versions of WTCII appear in two distinct phases, reflecting various factors that surrounded the composer's life. Through a close examination of the most famous Bach manuscript in Britain, the 'London Autograph', the authors gather evidence which enables them to reconstruct Bach's working strategy, as well as the stages of revision of the manuscript and how the work is left 'incomplete'. Many attempts were made by later generations to present WTCII as a finished product, but their limited knowledge of both the composer's style of compositions and the primary sources of the work made this an impossible task. Nevertheless, the close examination here of their attempts reveal fascinating aspects of their idealised views of Bach and his work, which in turn reflect the changing tide of the history of Western music.