The presence of antibodies to TSH receptor (TSHR) is the hallmark of Graves disease (GD). These antibodies mimic the action of TSH, resulting in TSHR stimulation and hyperthyroidism, and have been associated with GD-associated extrathyroidal manifestations. TSH binding inhibition assays and bioassays for measurement of TSHR antibody levels have been used for clinical and research purposes. In the former, inhibition of TSH binding to purified or recombinant TSHR by a patient's immunoglobulins is measured by radioactive or chemiluminescent techniques. In the latter, cyclic AMP production is measured by use of radioimmunoassays or chemiluminescent methods in cells natively or artificially expressing TSHR. In this Review, the different techniques used for the detection of antibodies to TSHR are discussed, together with the clinical applications of antibody measurement, including diagnosis of GD and Graves ophthalmopathy. Prediction of relapse after medical treatment and the clinical course of Graves ophthalmopathy are also addressed.