Optogenetics and photostimulation technologies enable precise, light-based control of cellular and neural activity with high temporal and spatial resolution. These approaches have become foundational tools for interrogating biological function across scales, from single cells to intact neural circuits. The applications highlighted on this page span cell-biology optogenetics, in vivo neuroscience optogenetics, and ex vivo/in vitro neuroscience optogenetics, reflecting the versatility of light-driven modulation in both basic and translational research. In addition, photoactivation techniques expand these capabilities by enabling targeted triggering of biochemical or signaling events within defined regions or populations. Together, these methods provide researchers with powerful strategies to dissect dynamic biological processes in real time.