Recently emerging mechanochromic systems are becoming highly attractive for structural health monitoring (SHM) purposes in various industries, such as civil, wind, and aerospace, to improve the safety and performance of structures. These are based on self-reporting polymer composites which provide a light-weight sensor with an easy-to-read visual cue for SHM purposes. The present paper reports a critical overview of mechanochromic self-reporting approaches and discusses the outlook for future development in the field. Design principles and cutting-edge applications of the main physical- and chemical-based self-reporting mechanisms, i.e., mechanochromism based on dye-filled materials, modified polymers, structural color materials, and smart hybrid composite sensors, are presented with special attention to SHM. These emerging sensors create a new generation of user-friendly, cheap, and power-free SHM systems, guaranteeing economic and technological advantages that will open up new horizons for innovative, safer, and lighter composite products with significantly lower maintenance costs.