Novel molecular motifs named immunoreceptor tyrosine-based inhibition motifs (ITIMs) have recently been recognized in the intracytoplasmic domains of an 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 potential clinical applications. The present volume contains 15 reviews written by authors who made significant contributions to the identification of ITIM-bearing molecules and the study of their biological properties.