A great deal of talent has been called upon over the past decade to try and understand the structure and the function of different types of foldases; as a result, remarkable insights into how these enzymes work has been gained. Recently the main focus of research has begun to shift to unveiling the precise role of these folding catalysts in many different processes in which they are involved inside the cell. It is becoming increasingly clear that the cellular functions of foldases go far beyond accelerating the folding of proteins. This is undoubtedly an area where one can expect significant research efforts in the next few years. The present book summarizes the current state of knowledge as to the structural and functional properties of four major types of foldases listed above. In structuring the material the author has sought to maintain a balance between historical development and current understanding, while also trying to look to the future and anticipate where the field is likely to move.