T-cell antigen receptors composed of γ and δ polypeptide chains (γδTCRs) can directly recognize antigens in the form of intact proteins or non-peptide compounds, unlike αβTCRs, which recognize antigens bound to major histocompatibility complex molecules (MHC). About 5% of peripheral blood T cells bear γδTCRs, most of which recognize non-peptide phosphorylated antigens1,2. Here we describe the 3.1 Å resolution structure of a human γδTCR from a T-cell clone3 that is phosphoantigen-reactive. The orientation of the variable (V) and constant (C) regions of the γδTCR is unique when compared with αβTCRs or antibodies, and results from an unusually small angle between the Vγ and Cγ domains. The complementarity-determining regions (CDRs) of the V domains exhibit a chemically reasonable binding site for phosphorylated antigens, providing a possible explanation for the canonical usage of the Vγ9 and Vδ2 gene segments by phosphoantigen-reactive receptors. Although the γδTCR V domains are similar in overall structure to those of αβTCRs, γδTCR C domains are markedly different. Structural differences in Cγ and Cδ, and in the location of the disulphide bond between them, may enable γδTCRs to form different recognition/signalling complexes than αβTCRs.