The essentials of radiation damage in metals and alloys are reviewed with special emphasis on the spatial distribution of the vacancies and interstitials produced. These concepts are then related to our current understanding of the phenomena of radiation hardening, radiation embrittlement, radiation creep, radiation swelling, and radiation growth. It is concluded that radiation hardening and radiation embrittlement in thermal reactors and at lower temperatures in fast reactors are best gauged by a measure of the number of primary knock-on atoms having an energy greater than some threshold energy. The other phenomena mentioned are best gauged as rate processes proportional to the rate of point defect production. No one gauge of radiation damage is best for all phenomena.