We address the dynamics of electronic–vibrational excited states in isolated molecules, clusters, condensed phase and biosystems, which pertain to the phenomena of energy acquisition, storage and disposal as explored from the microscopic point of view. The advent of femtosecond dynamics opened up new horizons in the exploration of chemical and biophysical processes on the timescale of nuclear motion. These ultrafast radiationless processes involve isolated molecules, where ultrafast ‘nonreactive’ intramolecular internal conversion can occur on the timescale of vibrational motion, while ‘reactive’ dissociation and Coulomb explosion manifest the sliding down on the repulsive nuclear surface. In some cluster and condensed phase systems ultrafast energy dissipation processes, manifesting collective large nuclear configurational changes, bear analogy to the molecular ‘reactive’ dynamics, but can concurrently maintain vibrational phase coherence induced by nuclear impact. For ultrafast dynamics in clusters, in the condensed phase and in the protein medium, separation of timescales for nuclear dynamics may prevail. Interstate and energy relaxation are understood, while the interplay between relaxation and dephasing is of considerable interest. The ubiquity of vibrational and electronic coherence effects, ranging from small to huge systems, raises the conceptual question of the distinction between the experimental conditions of the preparation and interrogation, and the intrinsic aspects of relaxation and dephasing dynamics. These are some of the central aspects of the novel and fascinating area of femtosecond chemistry, whose conceptual framework rests on a unified theory and simulation of intramolecular, cluster, condensed phase and biophysical dynamics.