Spectroscopy studies the interaction between light and matter. Ultrafast spectroscopy involves the study of this interaction using temporally short light pulses capable of probing directly the dynamics of the system rather than its energy levels. Rapid advances in laser technology over the past decades have resulted in the generation of pulses with femtosecond time duration (1fs = 10
−15
s). These lasers are being used to interrogate solids, liquids, and gases to learn about the dynamics of matter (electrons, atoms, molecules) following laser excitation. The description given here explains how an ultrashort laser pulse excites a coherent superposition of energy levels, and how this excitation can be followed in time. To date, ultrafast spectroscopy has been used to measure processes in diverse fields, for example, to measure the time it takes to break or form a chemical bond; to measure the temporal response of molecules involved in photosynthesis, or vision; and to measure the flow of charge in semiconductors. Examples of these kinds of studies illustrate this presentation.