In this review we describe several examples concerning the attractive properties of smart polymer composites containing aggregachromic dyes of different nature and structure. The dye–polymer interphase interactions depend on the equilibrium between the aggregated and the isolated forms of chromophores dispersed within the polymer matrix. Such interactions are easily perturbed by external solicitations like mechanical or thermal stresses, which induce a clear and rapid change in the composite’s optical properties both in absorption and in emission. These new stimuli-responsive composite materials therefore appear promising for the development of smart and intelligent polymer devices for sensing and safety applications.