Intraarticular injection of β-emitting radionuclides, called radiation synovectomy or radiosynoviorthesis, is an effective treatment in patients suffering from inflammatory-rheumatoid and degenerative joint diseases. Since the first description of intraarticular radionuclide therapy in 1952, several gamma- and beta-emitting radionuclides have been used in both experimental and clinical studies. Today, mainly three substances are in clinical use, each of them for special joints regarding to their biophysical characteristics: Yttrium-90 for knee joints, Rhenium-186 for mid-sized joints like shoulder, wrist or ankle joints and Erbium-169 for small joints of fingers and toes. Except for Rhenium, which consists of an additional gamma-radiation, all nuclides are pure beta-emitter with a tissue penetration depth of a few mm to avoid radiation damage to other diarthrodial tissues. Indication for radiosynoviorthesis is based on both clinical symptoms and on acute synovitis, proven in a pretherapeutic three-phase bone scan. Following intraarticular injection, the radionuclides are taken up by the synovial lining cells. A colloidal preparation with a mean particle size between 100nm and 2μm favors cellular uptake and minimizes extraarticular leakage by lymphatic or venous drainage. The local high energy irradiation results in sclerosis and fibrosis of the inflamed synovial membrane, achieving significant reduction of pain and joint effusion in appr. 70% of the patients. Present-day studies and future developments do focus in part on radiochemical aspects like new radionuclides with promising biophysical characteristics to optimize therapeutic effects with minimizing radation burden. Clinically oriented studies search for combined therapeutic approaches, e.g. the benefit of endoscopic synovectomy prior to radiosynoviorthesis.