Radiosurgery, or stereotactic radiosurgery, is a minimally invasive modality to treat a lesion with stereotactically focused ionizing radiation without surgical incision. Because there are no incision procedures, general anesthesia or transfusion is not required, and complications related to incisional procedures do not occur in radiosurgery. As a result, radiosurgery shows much low rates of complications than conventional open surgery with comparable cure rates. In the beginning, radiosurgery was applied only to a few intracranial diseases because a stereotactic frame was applied to the skull. Along with the development of technologies and accumulation of knowledge on radiosurgery such as medical imaging, computer, radiation physics, and radiobiology, indications of radiosurgery have been expanded in various ways. Nowadays, radiosurgery is accepted as an adjuvant treatment or a primary treatment option for many neurosurgical diseases and cancers. Cranial nerve schwannomas, brain meningiomas, pituitary adenoma, and other benign brain tumors are good indications for radiosurgery. Intracranial arteriovenous malformation, brain metastases from extracranial cancers, and trigeminal neuralgia are also well controlled by radiosurgery. Spinal metastases and various cancers are emerging indications for extracranial radiosurgery, which has been recently introduced. In this article, the authors summarized the basic concept, history, development, and future of radiosurgery as an introduction to radiosurgery.