A review is presented of recent developments in x-ray photon detectors and in the associated detector electronics. The first portion of the paper is devoted to a survey of the presently available physical information on the “intrinsic” resolution of silicon and germanium radiation detectors, proportional counters and NaI(Tl) scintillation crystals. Semiconductor detectors suitable for x-ray applications and low noise electronics are then analyzed in some detail. Discussions follow on scintillation detectors, proportional counters, and “external” photo-electric detectors. Recent spectral achievements and interesting applications are illustrated. Copyright © 1968 by The Institute of Electrical and Electronics Engineers, Inc.