The Chorale Cantatas by Johann Sebastian Bach are outstanding examples of his ingenuity. The existing data on the Chorale Cantatas are distributed throughout numerous volumes by many scholars. They have written much about the cantatas in general but not so much specifically about the chorales in them. In this thesis, the emphasis is on the chorales and Bach's treatment of them in the Chorale Cantatas. An historical approach to the cantata and the chorale is given as a preliminary to the treatment of the chorale in the chorale cantata. This was done that the reader might have a better understanding of them. The necessary material for this thesis was gathered from dictionaries, music lexicons, books, articles and the music principally in the Bach-gesellschaft edition. The material is organized according to the following plan: 1. The Church Cantata and its origin; the development of the Church Cantata in Germany; the use of the cantata in the worship service. 2. The Chorale, its origin and development; its changes as a result of the Reformation; its use in church services, and its use in musical composition. 3. Bach's treatment of the Chorale in musical forms. 4. Bach's treatment of the words of the Chorales in the Chorale Cantatas.