Diaryl ethers in which one of the aryl groups is a phenyl fused to a cycloalkyl or heterocyclic ring, to which is attached an acetic acid group, are agonists of G-protein coupled receptor 40 (GPR40) and are useful as therapeutic compounds, particularly in the treatment of Type 2 diabetes mellitus, and of conditions that often accompany this disease, including insulin resistance, obesity and lipid disorders.