The ζ family includes ζ, η, and FcεRIγ (Fcγ). Dimers of the ζ family proteins function as signal transducing subunits of the T cell antigen receptor (TCR), the pre-TCR, and a subset of Fc receptors. In mice lacking ζ/η chains, T cell development is impaired, yet low numbers of CD4+ and CD8+ T cells develop. This finding suggests either that pre-TCR and TCR complexes lacking a ζ family dimer can promote T cell maturation, or that in the absence of ζ/η, Fcγ serves as a subunit in TCR complexes. To elucidate the role of ζ family dimers in T cell development, we generated mice lacking expression of all of these proteins and compared their phenotype to mice lacking only ζ/η or Fcγ. The data reveal that surface complexes that are expressed in the absence of ζ family dimers are capable of transducing signals required for α/β-T cell development. Strikingly, T cells generated in both ζ/η−/− and ζ/η−/−-Fcγ−/− mice exhibit a memory phenotype and elaborate interferon γ. Finally, examination of different T cell populations reveals that ζ/η and Fcγ have distinct expression patterns that correlate with their thymus dependency. A possible function for the differential expression of ζ family proteins may be to impart distinctive signaling properties to TCR complexes expressed on specific T cell populations.