This chapter provides a concise introduction to Efimov physics that is easily accessible to a nonspecialist. We discuss three-body physics in ultracold quantum gases and place these ideas in a wide context touching nuclear, atomic, and molecular physics. The last part deals with similarities and differences between three-body systems that consist of identical particles (homonuclear) or particles with different masses (heteronuclear). These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.