Brachytherapy has the potential to ubiquitously deliver high doses of radiation to the target with a steep dose gradient without traversing the normal tissues. This chapter provides an overview of the fundamental principles, historical development, and technological advancements that have revolutionized brachytherapy. Advancements in imaging technologies, including ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), have been pivotal in enhancing the accuracy of brachytherapy. These modalities have facilitated precise tumor localization, treatment planning, and a better toxicity profile. The workflow of brachytherapy involves several intricate steps, including case selection, comprehensive clinical and radiological mapping, principles of treatment planning, and delivery. Future direction for further advancements focuses upon knowledge-based planning, electromagnetic tracking, and biological optimization.