The T cell receptor-CD3 (TCR/CD3) complex is a multichain structure in charge of antigen recognition in T cells. Despite many genetic, structural, and functional data obtained in recent years, essential questions concerning the TCR/CD3 complex still remain open, including: 1) the precise number of polypeptides in each TCR/CD3 complex, their interactions and spatial arrangement, 2) the role(s) of each polypeptide in antigen recognition and/or in receptor signal transmission, and 3) the relationship between the TCR/CD3 complex and other membrane or cytoplasmic molecules involved in downstream signaling. In this work we shall review data concerning some of these issues, proposing a model of the overall structure of the TCR/CD3 complex to explain its known features.