The handbook aims to provide a comprehensive resource for understanding ionizing radiation dosimetry, catering to experts, policymakers, and interested readers. The content of the handbook is focused on two main aspects of dose measurements: external dosimetry and internal dosimetry. The section on external dosimetry covers fundamental principles and discusses monitoring techniques across various environments, such as nuclear, industrial, research, and medical facilities. It also covers advanced topics like Bayesian inference and retrospective dosimetry. The internal dosimetry section explores radionuclide biokinetics, simulation techniques, dose evaluation, and monitoring methods. Specific scenarios, such as radon inhalation and off-normal conditions, are addressed, highlighting the importance of precision and intervention. The handbook serves as a comprehensive resource for students, academicians, scientists, engineers, and policymakers interested in seeking an in-depth knowledge of radiation dose measurements and its multi-faceted aspects in protecting human health and the environment.