Early Times of Photochemistry.- The Framework of Photochemistry: The Laws.- The Framework of Photochemistry: State Diagram.- Some Paradigmatic Topics.- The Role of Photochemistry in Chemistry.- Photochemistry, a Powerful Science.- Of Excited States, Again.- Photochemical and Photocatalyzed Synthesis.- Medicinal and Diagnostic Applications.- Solar Energy Conversion.- Actuators.- Photochemistry and Green Chemistry.