Recent applications of the electrostatic, electron multiplier tube to problems which require the measurement of very small currents or the counting of single ions or electrons are described in this paper. The characteristics of secondary electron emitting surfaces suitable for use in multiplier tubes are discussed in the first section. The next section is devoted to recently developed tubes having one or more stages of electron multiplication. Following this is a section dealing with the application of these tubes to problems involving electron and ion counting. The paper is concluded by a section on the statistical treatment of the distribution in pulse sizes from multiplier tubes.