Interactions of molecules with light play a fundamental role in nature, where photons usually act on the molecules and drive chemical reactions and other processes. However, when confined to sub-wavelength regions, the interaction with light can be enhanced up to the point where the quantum-coherent interactions overcome all other processes. In this "strong coupling regime" the light and the molecules start to behave as a single entity, having its own quantum states and energy levels. In my talk I will present the fundamental physics of strong coupling in hybrid organic-photonic structures, and how it can be used to control the properties of organic materials and their chemical behavior.