Cbl proteins are important ubiquitous regulators of various biological processes ranging from defense against infection to bone formation, and the list of these processes grows continuously. There are three Cbl-family proteins in mammals, which exhibit disparate biological effects. Furthermore, all metazoans appear to have Cbl-like proteins playing important regulatory roles in these organisms ranging from round worms and flies to amphibians and birds. One of the interesting peculiarities of the Cbl-mediated regulation is its dependence on multiple molecular mechanisms, which makes this regulation complex and difficult to comprehend. In spite of the considerable progress in the understanding of the Cbl family and its functions, which was achieved not without some unexpected and dramatic turns, Cbl proteins remain rather enigmatic. This book presents an in-depth analysis of the current state of knowledge on this subject. It discusses structure, functions and mechanisms of action of Cbl proteins, including biological and clinical implications of this knowledge. This important book can serve as a good primer for those who wish to enter the area of Cbl research, as well as a convenient reference for those already working in it.