Time-resolved optical spectroscopy has developed rapidly in recent years, and the development of various types of lasers for ultrashort light pulses has enabled spectroscopists to increase the temporal resolution to the picosecond, and even femtosecond, range. The field of ultrafast spectroscopy, while still in its early stages, is evolving rapidly and a compilation of methods and results, their classification and critical evaluation is therefore greatly in demand. This book meets that need by summarizing and classifying current knowledge on the application of ultrafast optical methods in photophysics, photochemistry, photobiology and other related fields. Written in textbook style, it begins with a short summary and discussion of the relevant methods and devices, ranging from millisecond flash photolysis to femtosecond devices, and covering the detection of short-lived intermediates by time-resolved Raman spectroscopy. This is followed by a detailed description of data analysis and interpretation of results for various experimental methods. The authors discuss very thoroughly the precision of experimental data, the potential of data-acquisition systems and the necessity of combining various experimental methods in order to investigate complex processes. Applications are discussed from the point of view of scientists interested in the detection and investigation of (photo)reactions by means of time-resolved optical methods. The processes occurring in photophysics, photochemistry and photobiology are therefore described in connection with the information available from time-resolved optical spectra. The book is suitable both as an advanced text for students of physics and chemistry, and as a reference work for professional spectroscopists. It provides them with an introduction to the variety of processes occurring after excitation of molecules and a thorough understanding of the potentials and limitations of various ultrafast spectroscopic methods which are used to observe these processes.