In the fight against cancer, radiation therapy plays a vital role, with its two essential approaches: internal, involving the insertion or implantation of radioactive material into the patient’s body, or uptake of radiopharmaceutical, and external. Precise delivery of the appropriate radiation dosage to the tumor is critical for achieving favorable outcomes. This is where dosimetry becomes crucial—a scientific discipline that involves measuring, calculating, and evaluating radiation doses. Medical physicists utilize dosimetry to ensure the accuracy and proper calibration of machines that administer ionizing radiation, ensuring safety. This chapter provides a brief overview of advanced techniques and equipment used in dosimetry, with a primary focus on photon and electron dosimetry, the most widely employed forms of radiation for radiotherapy worldwide.