This chapter explores the fundamental principles, types, and practical applications of scintillators in the detection and measurement of ionizing radiation. The chapter outlines the scintillation mechanisms in both organic and inorganic scintillators, detailing how their material properties influence performance characteristics like stability, reproducibility, linearity to dose, and radiation hardness. The challenges introduced by the stem effect are discussed, along with various correction methods. Emphasis is placed on the water equivalence of organic scintillators, making them ideal for medical applications where tissue equivalence is critical. Furthermore, the chapter presents a comparative analysis of commercial and in-house scintillation detectors, highlighting their clinical relevance in small-field dosimetry and emerging use in brachytherapy and ultra-high-dose-rate applications. Current applications with commercial products are also presented.