Chemical reactions take place over an amazingly rapid time-scale, measured in millionths of a billionth of a second (a femtosecond). On time-scales of this duration, atoms and molecules come together, exchange energy and transfer atoms in the very act of transforming one substance into another. The emergence during the last ten years of laser devices that emit bursts of light just a few femtoseconds long can, however, enable scientists to record a series of ‘snapshots’ in real time of the entire temporal development of chemical reactions, and to understand their dynamical evolution during the critical moments when bonds are broken and made. This article reviews the application of femtosecond lasers to the study of the dynamics of chemical reactions, and attempts to show how a close synergy between calculations and experiment enables the forces that control the conversion of reactants into products to be understood in terms of fundamental quantum theory. This is illustrated through consideration of a hierarchy of problems, starting with photochemistry in gases, catalytic processes at metal surfaces, and ending with processes in the condensed phase. A speculative conclusion forecasts developments in new laser techniques, highlighting how the exploitation of ever shorter laser pulses would permit the study and possible manipulation of the nuclear and electronic effects that lie at the conceptual heart of chemistry.