Optogenetics is a transformative technology enabling the mapping of neural circuits with greater cellular specificity and spatio-temporal resolution than previously possible. It was named Method of the Year by Nature Methods in 2010, and its inventors awarded the The Brain Prize 2013 by the Grete Lundbeck European Brain Research Foundation; a Nobel Prize is likely to follow. We have invented a neural probe that is uniquely suited to optogenetic interrogation of the brain. Consisting of integrated thin film electrodes on a fine optical fiber, it provides lossless light delivery, minimal insertion damage to brain tissue, and the ability to probe deep brain structures, each of which is lacking in currently available probes.