This monograph features what happens when light meets molecules. This edited volume contains contributions from an international array of contributors, and it is divided into sections representing a selection of carefully focussed and connected photochemistry topics: energy, technology, medicine, environmental sciences, and art. In each section one or more chapters illustrates relevant aspects of each field, such as artificial photosynthesis and solar energy conversion (energy), light emitting devices and photochromic dyes (technology), and photodynamic therapy and solar filters (medicine). Aimed at students of all levels and researchers active in photochemistry.