Controlling activity of defined populations of neurons without affecting other neurons in the brain is now possible by a new gene- and neuroengineering technology termed optogenetics. Derived from microbial organisms, opsin genes encoding light-activated ion channels and pumps (channelrhodopsin-2 [ChR2]; halorhodopsin [NpHR], respectively), engineered for expression in the mammalian brain, can be genetically targeted into specific neural populations using viral vectors. When exposed to light with appropriate wavelength, action potentials can be triggered in ChR2-expressing neurons, whereas inhibition of action potentials can be obtained in NpHR-expressing neurons, thus allowing for powerful control of neural activity. Optogenetics is now intensively used in laboratory animals, both in vitro and in vivo, for exploring functions of complex neural circuits and information processing in the normal brain and during various neurological conditions. The clinical perspectives of adopting optogenetics as a novel treatment strategy for human neurological disorders have generated considerable interest, largely because of the enormous potential demonstrated in recent rodent and nonhuman primate studies. Restoration of dopamine-related movement dysfunction in parkinsonian animals, amelioration of blindness and recovery of breathing after spinal cord injury are a few examples of such perspectives.