Radioisotopes are radioactive isotopes of elements that are used widely in medicine, industry, and research. They occur naturally or can be artificially produced. In medicine, radioisotopes are used in diagnostic tests and cancer treatments due to their short or long half-lives. Examples used are iodine-123 for thyroid disorders and cesium-137 for cancer treatments. Industry uses radioisotopes for non-destructive testing of materials and structures as well as measuring levels and thicknesses. Research employs radioisotopes to study biological and chemical processes. Common radioisotopes and their medical and research applications are described.