Caesium-137 has a number of practical uses. In small amounts, it is used to calibrate radiation-detection equipment. In medicine, it is used in radiation therapy. In industry, it is used in flow meters, thickness gauges, moisture-density gauges (for density readings, with americium-241/beryllium providing the moisture reading), and in gamma ray well logging devices.
Caesium-137 is not widely used for industrial radiography because it is hard to obtain a very high specific activity material with a well defined (and small) shape as caesium from used nuclear fuel contains stable caesium-133 and also long-lived caesium-135. Isotope separation is too costly compared to cheaper alternatives. Also the higher specific activity caesium sources tend to be made from very soluble caesium chloride (CsCl), as a result if a radiography source was damaged it would increase the spread of the contamination. It is possible to make water insoluble caesium sources (with various ferrocyanide compounds such as , and ammonium ferric hexacyano ferrate (AFCF), Giese salt, ferric ammonium ferrocyanide but their specific activity will be much lower. Other chemically inert caesium compounds include caesium-aluminosilicate-glasses akin to the natural mineral pollucite. The latter has been used in demonstration of chemically stable water-insoluble forms of nuclear waste for disposal in deep geological repositories. A large emitting volume will harm the image quality in radiography.  and , are preferred for radiography, since these are chemically non-reactive metals and can be obtained with much higher specific activities by the activation of stable cobalt or iridium in high flux reactors. However, while  is a waste product produced in great quantities in nuclear fission reactors,  and  are specifically produced in commercial and research reactors and their life cycle entails the destruction of the involved high-value elements. Cobalt-60 decays to stable nickel, whereas iridium-192 can decay to either stable osmium or platinum. Due to the residual radioactivity and legal hurdles, the resulting material is not commonly recovered even from "spent" radioactive sources, meaning in essence that the entire mass is "lost" for non-radioactive uses.
As an almost purely human-made isotope, caesium-137 has been used to date wine and detect counterfeits and as a relative-dating material for assessing the age of sedimentation occurring after 1945.
Caesium-137 is also used as a radioactive tracer in geologic research to measure soil erosion and deposition; its affinity for fine sediments is useful in this application.