The paper is a review of the techniques used in the detection and measurement of very-short-wave radiations (X-rays and γ-rays) and nuclear and cosmic particles (α-particles, β-particles, protons, neutrons and mesons).The radiations and particles are classified under three headings—X-rays and γ-rays, charged particles, and uncharged particles; in each case an account is given of the more important measurable quantities (e.g. energy,W, flux of radiation, Φ, radiation dosage,r, etc.) and the physical basis of the method of measurement involved. The examples chosen to illustrate these techniques are process instruments developed at the Atomic Energy Research Establishment to provide continuous monitoring of α- and β-activities in solution. In the α-activity monitoring instrument the pulse technique is used for recording individual particles, whereas in the β-activity instrument the mean rate of ionization in an ionization chamber is measured as a direct current. Complete descriptions are given of both instruments, together with details of the performance characteristics obtained.The paper ends with a discussion of nucleonic-instrument design, and a number of aspects receive special mention, namely sourcedetector geometry, detectors in assay instruments, special problems associated with portable instruments and, lastly, materials and finishes for radioactive-contamination monitoring instruments.