This review is about the physiological and non-redundant functions of the PKC gene products in hematopoietic cells, particularly T cells. In spite of the large amount of information on PKC functions in various cell types and tissues, the characterization of the isotype selective functions of the entire PKC family in lymphoid cell lineages is far from complete. Given the established important role of PKCθ as regulator of T cell fate and knowing that several other PKC isotypes are also expressed in T cells at a high level, we here summarize the physiological and non-redundant functions of PKCα, β, δ, ε,ζ and θ isotypes in T cells (with emphasis on the ongoing mouse genetic studies). Their known and/or suspected cellular regulation, effector pathways as well as physiological functions are discussed. While PKCβ,ε, δ and appear to be dispensable during cellular activation of primary CD3+ T cells, PKCα and PKCθ take critical parts in signaling pathways that are necessary for full antigen receptor mediated T cell activation and T lymphocyte immunity.