G protein-coupled receptors (GPCRs) are the largest class of eukaryotic membrane proteins. They trigger intracellular signalling cascades by activation of heterotrimeric G proteins. They are of great pharmaceutical interest, with approximately 40% of marketed drugs targeting GPCRs. It has been shown that GPCRs can form oligomers in phospholipid bilayers in vivo and in vitro, affecting both ligand binding and G protein coupling [1].Neurotensin receptor 1 (NTS1) is one of few GPCRs that can be produced in E. coli in an active state, and has been implicated in conditions such as schizophrenia and Parkinson's and postulated as a biomarker for various cancers [2]. NTS1 has been shown to dimerise in lipid bilayers [3], and though a crystal structure of NTS1 in detergent was recently published [4], there is still no structural data on the receptor and its dimer in a membrane environment.We use a range of biophysical techniques to characterize the structure and function of NTS1 in model membrane systems, including ensemble and single molecule Forster resonance energy transfer (FRET), and double electron-electron resonance (DEER, also known as PELDOR). Fluorescence or nitroxide spin probes are attached to engineered cysteines on the transmembrane helices. By measuring intradimer distances between the probes on each monomer, we are studying dimerisation behaviour of NTS1 to produce a model of its dimeric structure in a more native lipid environment.