The electron microprobe (EMP) is an electron optical instrument in which compositional and topographic information are obtained from regions ⩽1μm in diameter on a specimen. Photographs of compositional and topographic changes in 1-mm²to 20-μm² areas on various types of specimens can also be obtained which are strikingly similar to optical photomicrographs. This paper discusses the various signals that are measured in the EMP (X-rays, secondary electrons, backscattered electrons, etc.), their resolution, and the types of information that can be obtained. In addition to elemental analysis, the solid state detector and scanning techniques will be discussed. The last sections will cover characterization of phases-homogeneity-trace element analysis-quantitative metallography and various techniques which extend the instrument capabilities such as deconvolution and soft X-ray analysis. Various applications will be discussed and illustrated.