Prompt γ‐activation analysis (PGAA) is a rapidly developing nuclear analytical technique for the determination of elemental and isotopic composition. The largest neutron research centers and many smaller research reactors operate in‐beam PGAA instruments for the purpose of a wide variety of analyses. PGAA is a nondestructive analytical technique and is suitable for the analysis of light elements, especially hydrogen and boron, as well as some trace elements (e.g. rare earths and cadmium). Because of the deep penetration of both neutrons and γ‐rays, PGAA is suitable for the analysis of samples in closed containers. As the technique is nondestructive and does not require any sample preparation, it is especially useful for the investigation of precious objects (e.g. archaeological artifacts) or hazardous materials. The basic principles of the method, the instrumentation, and some basic issues of the installation, and operation of the in‐beam PGAA technique are all described in this article. A few typical applications are also introduced.