Luminescent molecular aggregates, called J‐aggregates, are an interesting example of supramolecular structures with a number of unique spectral properties. Their optical properties are governed by the excitonic nature resulting from high‐order molecular packing in the J‐aggregate chains. The J‐aggregate characteristic feature is the bathochromically shifted narrow excitonic band termed the J‐band. The optical properties of J‐aggregates are markedly distinct from those of the individual molecules forming the aggregate, namely narrow absorption band, high oscillator strength, giant third‐order susceptibility, resonant luminescence, and effective exciton diffusion. Although solutions of J‐aggregates often possess low photostability for practical usage, their solid samples are more convenient, especially different polymer films due to their ease of preparation and availability of application. J‐aggregate formation in polymer films has both advantages and disadvantages: Some spectral characteristics could degrade, whereas composites creation could modify and improve their optical properties. This article aims to demonstrate how the interaction of J‐aggregates with polymers in both solution and solid film state affects their spectral properties. In addition, examples of composites and devices based on polymer‐bound J‐aggregates are discussed.