Radiation dosimetry is a Ÿeld of radiation detection devoted to the quantitative measurement of the physical changes that occur in matter upon exposure toionizing radiation. Radiation dosimetry is performed on aroutine basis toensure the occupational safety of workers when there exists arisk of radiation exposure. Such routine personal dosimetry is used to monitor and limit the long-term occupational exposure to workers and to assist with the assessment of the dose received in the event of an accidental exposure. Some occupations that have an associated risk of radiation exposure include medical personnel performing clinical x-ray diagnostic and radiotherapy procedures and military and civilian personnel involved in power plant maintenance and operation. Radiation dosimetry is also an important tool in awide range of environmental monitoring and industrial processing applications. œe scope of this chapter is limited to discussion of the most widely used and commercially available technologies for dosimetry of ionizing radiation for personal protection; however, it should be recognized that many of the same technologies are used with equal e¥ectiveness for other dosimetry applications.