Since 1910, when Lespinasse [73] in Chicago was the first surgeon to use an endoscopic device for the treatment of a neurologic disease, various methods of endoscopy have evolved into accepted diagnostic and therapeutic adjuncts of modern neurosurgery. Nevertheless, until recently technical shortcomings of the available endoscopes have prevented the widespread use of neuroendoscopy. However, now, at the end of the 20th century, endoscopes can be regarded as some of the most important instruments for the development of microneurosurgery into the 3rd millennium. The aim of this review of intracranial endoscopy in neurosurgery, which admittedly might not be completely objective in the authors' personal assessment of various endoscopic techniques, is first to depict the historical evolution of neuroendoscopy, second to describe the technical equipment used in intracranial endoscopic neurosurgery, third to characterize the most frequent endoscopic methods in brain surgery, and fourth to indicate how neuroendoscopy might develop in the near future. It will be shown that this ongoing evolutionary process in neuroendoscopy was only possible with the mutual influence of improved diagnostic techniques, increased microanatomical knowledge, refined neurosurgical instrumentation--especially the introduction of the surgical microscope, and endoscopic diagnostic and therapeutic strategies.