- Photodissociation studies of vibrationless ground state molecules pervade diverse areas of chemical physics, while those of rovibrationally excited molecules are expected to have even more impact due to the additional fascinating possibilities they offer and the new horizons they open. Photodissociation of rovibrationally excited species involves a double-resonance scheme in which a photodissociative transition is initiated from an excited rovibrational state that might substantially affect the intensity and wavelength dependence of the photoabsorption spectrum. In favourable cases, when the energy is disposed in vibrations that are strongly coupled to the reaction coordinate, this pre-excitation might influence photodissociation pathways and lead to selective bond cleavage. In other cases it might influence the branching ratio between different fragments by altering the photodissociation dynamics. Moreover, the photodissociation of rovibrationally excited species can serve as a sensitive means for detection of weak vibrational overtone transitions of jet-cooled molecules, and therefore a promising way for revealing specific couplings and time evolution of the prepared vibrational states. Experimental studies on different polyatomics are used to demonstrate the above aspects and to show how the mechanism of chemical transformations and the nature of rovibrationally excited states are highlighted by photolysis of these pre-excited molecules.