Interleukin-15 muteins and other interleukin-15-related molecules are described, as well as methods of identifying interleukin-15 muteins and other interleukin-15-related molecules. Also described herein are modifications of the foregoing, which modifications may enhance a property (e.g., half-life) of the muteins or other molecules compared to human interleukin-15. Pharmaceutical compositions and methods of use are also described herein.