This book reviews recent work on molecular chaperones of the prefoldin family from their discovery in Archaea to the basic clarification of their structure. Even though, there is still a lot to investigate in order to understand the roles and functions of prefoldins, some preliminary work suggests their contribution in assembly and activation of a variety of macromolecular complexes. Hence, the reader is introduced to recent structural findings via cryo-electron microscopy and to the importance of this particular group of proteins in health and disease. This book also discusses the particular structure of the URI prefoldin-like complex. In addition, recent developments in the generation of URI mouse models speculate on the functions and emerging roles of the URI prefoldin-like complex in various cellular processes. This novel protein complex represents a unique cellular machinery, which molecular basis of its activity still remains to be determined. This work is thus a guide to help researchers in the field to have a more comprehensive and critical view of the prefoldin world.