This paper reviews the present state of development of X-ray excitation with radioisotope sources and of relevant methods of non-dispersive energy selection and X-ray detection. Reduction of interferences arising from absorption, enhancement and particle-size effects is also discussed. The compactness, cheapness and simplicity of the measuring head that result from the use of radioisotope excitation and non-dispersive energy selection are being exploited by portable and “on-stream” analysers now commercially available. The number of applications to ore and alloy analysis is already large and is increasing rapidly. The advantages of radioisotope X-ray spectrometry are less marked and less important in the laboratory where many facilities and alternative techniques exist. Nevertheless, applications for routine single-element determinations are increasing. The basic techniques of excitation and energy selection have been worked out but not yet evaluated for all possible applications. In many of the problems that have been studied, alternative excitation and detection methods have been used but not directly compared. Physical methods for overcoming absorption and enhancement effects have been developed, mainly by analogy with conventional X-ray spectrometry. Suppression of particle-size effects in the analysis of heterogeneous materials remains a problem, especially as fusion techniques for removing the heterogeneity are virtually restricted to the laboratory. There is scope for the development of new techniques for overcoming particle-size effects, especially in “on-stream” analysis.