Optogenetics represents a breakthrough technology capable of dynamically modulating molecular and cellular activity in live cells with high precision. This transformative technology made it possible to reversibly interrogate protein actions, cellular events, and animal behaviors with a simple flash of light. Manipulating the temporal and spatial profile of light enabled precise control of membrane potentials. This feature has inspired non-opsin-based optogenetics, which not only inherits the precise spatiotemporal resolution but also expands the targets into a diverse pool of biomolecules such as membrane receptors, ion channels, kinases, GTPases, and transcription factors. This book is unique because it emphasizes the design and applications of opsin-free optogenetic tools.