This chapter provides an in-depth overview of radiation physics, emphasizing its historical development, underlying principles, and relevance to dental imaging. It outlines the evolution of X-ray technology, advances in image quality, and the transition from film-based to digital radiography. Various imaging modalities—including intraoral, extraoral, cone-beam computed tomography (CBCT), computed tomography (CT), and nuclear medicine techniques—are discussed, with attention to their diagnostic applications in orofacial pain assessment. This chapter also addresses sources of radiation, comparative dose levels, biological effects, and comprehensive radiation protection strategies based on the As Low As Reasonably Achievable (ALARA) principle, ensuring patient and operator safety.