A number of physical phenomena related to reaction thresholds are discussed. Some history and some general remarks are included. The principal focus is on Coulomb‐bound systems, their formation in nuclear reactions, their structure, and their decay. Among the atom‐like systems considered are &pgr;A pionic atoms, Positronium, pionium (&pgr;+&pgr;−), and multipionic (N&pgr;A) atoms.