THE ADVENT OF the microscope in the operating room revolutionized neurosurgery. We traced the origin and evolution of this important invention from the first magnifying lens to its practical application in neurosurgery. The concept of magnification evolved from unexplained observations in ancient times to the invention of the microscope by the late 16th century. In the subsequent 3 centuries, scientists made technical advances that greatly improved the power and utility of the microscope. By the early 20th century, otolaryngologists became the first surgeons to use the microscope in clinical surgery. After World War II, opthalmologists and vascular and plastic surgeons began using the microscope in the operating room, making further technical improvements. It was a relatively small group of pioneering neurosurgeons in the late 1950s and 1960s who transformed microneurosurgery from a revolutionary and unorthodox "experiment" into the standard of care in much of modern neurosurgery.