Femtochemistry is the area of physical chemistry that studies chemical reactions on extremely short timescales (approximately 10−15 seconds or one femtosecond, hence the name) in order to study the very act of atoms within molecules (reactants) rearranging themselves to form new molecules (products).This anthology, which is adapted from the Nobel Lecture, gives an overview of the field of Femtochemistry from a personal perspective, encompassing our research at Caltech and focusing on the evolution of techniques, concepts, and new discoveries. In developing femtochemistrythe study of molecular motions in the ephemeral transition states of physical, chemical, and biological changeswe have harnessed the powerful concept of molecular coherence and developed ultrafast-laser techniques for observing these motions. Femtosecond resolution (1 fs = 10-15 s) is the ultimate achievement for studies of the dynamics of the chemical bond at the atomic level. On this time scale, matter wave packets (particle-type) can be created and their coherent evolution as a single-molecule trajectory can be observed. The field began with simple systems of a few atoms and has reached the realm of the very complex in isolated, mesoscopic, and condensed phases and in biological systems such as proteins and DNA. It also offers new possibilities for the control of reactivity and for structural femtochemistry and femtobiology.