Sumner Norman (Buck Institute for Research on Aging, formerly Caltech) delivers a comprehensive survey of neurotechnology from early EEG and deep brain stimulation through today's high-density electrode arrays and closed-loop BCI systems. He covers the engineering limits that have shaped the field — spatial resolution, biocompatibility, longevity of implants — and where breakthroughs in materials science, wireless transmission, and machine learning are opening new possibilities. A clear-eyed assessment of what is clinically viable now, what is 5–10 years away, and what remains fundamental science.