Radiation sources have been used in process control for over 40 years. Their use in inspection, implying visual examination, although of much earlier origin in the form of gamma radiography, is also of recent emergence in the form of tomographic methods. This paper firstly reviews the justification for the continued world-wide usage of isotopic methods. It then reviews a selection of innovative process control applications, based on radiation sources, as illustrations of the present state of the art and also describes recent progress in inspection methods including progress in the development of on-line facilities. For all applications involving radiation sources, careful selection of parameters is required to achieve the highest efficiency compatible with an integrity suitable for the intended application. The paper concludes with a brief discussion of the common principles on which the fabrication of sources is based in order to satisfy National and International safety legislation.