Optical methods offer a number of advantages for the study of neural systems. Optical techniques are relatively noninvasive, and offer wide field of view, in addition to high resolution in time and in space. Improvements in optical sensor technologies and imaging techniques continually enhance imaging performance, and extend resolution into three dimensions. Digital signal processing strategies allow increasingly subtle signals to be extracted and visualized. Imaging methods allow large populations of cells to be examined simultaneously, while resolving individual cells. Differential absorption or fluorescence emission by endogenous biochemicals or exogenous reporters allows characterization of specific aspects of the chemical and physical environment of cells, and produces signals that are highly correlated with neural activation. Fast intrinsic optical signals, which appear to be tightly coupled to the biophysical processes of neural activation, hold great promise for dynamic imaging of function in large populations of neurons. Coupled with multi-channel electrophysiological and computational modeling techniques, optical imaging enables powerful new understanding of the function of the brain.