T cell receptor (TCR) activation is a defining event in adaptive immunity. Yet almost 30 years after the discovery of its molecular components, the mechanism of TCR “triggering” is still unknown. This is largely due to the complexity of the receptor and a lack of structural information on the intact complex. In order to form a functional receptor that can be exported to the T cell surface, the ligand-sensing TCRαβ heterodimer must assemble with the CD3γε, CD3δε and ζζ signal-transducing modules. The spatial arrangement of these eight subunits within an intact complex is not known, but the best-characterised TCR-CD3 interactions are specific polar contacts within their transmembrane (TM) domains that are critical for assembly and surface expression. I have designed an in vitro translation-based disulphide scanning approach to map further points of contact between TCR and CD3 TM domains in the context of fully assembled complex. My data indicate that TCRα and β are closely associated and identify several contacts within this interface, about which essentially nothing was previously known. In addition, several TCR TM domain positions were identified that can crosslink to native cysteines in the TM domains of CD3δ and CD3ε. These observations are guiding our solution NMR-based efforts to determine a detailed structure of the TCRαβ TM domain complex and further map the positions of signalling modules around this central TCR “hub”. Elucidating the spatial arrangement of TCR-CD3 complex subunits will provide an instructive platform to understand how these components cooperate to transmit the crucial signals that activate T cells.