This text elucidates the achievements in calculating photodissociation cross sections and fragment state distributions from first principles, starting from multi-dimensional potential energy surfaces and the Schr?dinger equation of nuclear motion. Following an extended introduction in which the various types of observables are outlined, the next four chapters summarize the basic theoretical tools, namely the time-independent and time-dependent quantum mechanical approaches as well as the classical picture of photodissociation. The discussion of absorption spectra, diffuse vibrational structures, the vibrational and rotational state distributions of the photofragments form the core of the book. More specific topics such as the dissociation of vibrationally excited molecules, emission during dissociation, or nonadiabatic effects are discussed in the last third of the book.