The photophysics and photochemistry of betecarboline (9H-pyrido/3,4-b/indole) derivatives are systematically and comprehensively reviewed. Topics explicitly discussed include the influence of molecular structure (aromatically, substituents) and environmental effects (solvent, pH, temperature) on the electronic absorption, fluorescence and phosphorescence spectra, and on the lifetimes of the excited states. In a separate section we review the photochemistry of betacarbolines including their acid-base properties, the photoreactivity of their excited states, and their phototoxic properties.