Now firmly established as a versatile tool in many branches of science, the laser has taken little more than a decade to develop from a research project itself into an instrument for the support of other research. The number of laser applications in industry, technology and pure science is now so great that no one article could possibly cover them all. Here I will be concentrating on scientific applications only, but even so I must adopt a limited scope. The choice of topics has been restricted by posing the question: Of the many scientific investigations conducted with help from lasers, which ones are feasible only because lasers are available? Applications that satisfy this criterion should be the ones that best emphasize the unique capabilities of the laser as a tool of science.