Rho GTPases control many aspects of cell physiology. This includes polarity, endo/exocytosis, adhesion, motility, transcriptional activation, cell cycle progression or apoptosis. In view of such pleiotropic activities, Rho-controlled signaling has proven to be of medical relevance, especially in tumorigenesis, disease-associated bone remodeling and infectiology. This book is divided into three parts. Part 1 gives an evolutionary perspective of the Rho family, its atypical members, and an overview of how Rho activity is regulated. Part 2 addresses two important aspects of multicellularity controlled by Rho-dependent pathways, namely, cell-cell interactions and mechanotransduction. It also describes how post-translational modifications control Rho activity and how this is exploited by pathogenic bacteria. Part 3 explores several examples of the variety of pathophysiological processes controlled by Rho signaling, and gives a successful example of translational research, from the inhibition of Rho activation to the development of new molecules against osteoporosis. This updated review on the biology of Rho GTPases is an essential read for molecular and cell biologists. It is also an invaluable guide to post-graduate and medical students who wish to deepen their knowledge in cell biology.