Novel molecular motifs named Immunoreceptor Tyrosine-based Inhibition Motifs (ITIMs) have recently been recognized in the intracytoplasmic domains of a still-increasing number of receptors which control cell activation and proliferation. Research on ITIM-bearing molecules has developed exponentially during the last three years, generating new concepts with important consequences in basic research and with exciting potential clinical applications. The present volume contains 15 reviews written by authors who all made significant contributions to the identification of ITIM-bearing molecules and the study of their biological properties. It constitutes the first synthesis ever published that is specifically devoted to this emerging topic.