An optogenetic illumination system based on the use of a liquid crystal display projector and video tracking software is reported, which allows real-time multispectral light delivery with high spatial resolution to specified targets in freely moving Caenorhabditis elegans. Also in this issue, Leifer et al. report a similar illumination system using a digital micromirror device. Both methods allow optogenetic perturbation of a variety of neural circuits in the behaving worm.