Birkat Ha-Avoda of Tefillat Ha-Amidah has a long history spanning the Second Temple period to the early Middle Ages. This title follows the different formats of the prayer through the ages, examining a variety of sources: Writings from the Second Temple period, rabbinic texts, Christian texts, early Piyutim, medieval sources, and dozens of Siddurim and excerpts from Siddurim. The comparative study of these sources generates a detailed description of the development of Birkat Ha-Avoda, which sheds light on the history of the regular prayers and Jewish customs.