The versatility of optics enables the design of a wide range of elegant beam instrumentation. Multiple properties of particle beams can be precisely measured by various optical techniques, which include: direct sampling of optical radiation emitted from a charged particle beam; monitoring interactions with an optical probe such as a laserwire; and by electro-optic conversion of the beam signal with high-bandwidth fibre readout. Such methods are typically minimally-invasive and non-destructive, thus permitting diagnostics during accelerator operation without perturbation of the particle beam or risk of damage to the instrument. These proceedings summarise three CAS lectures that introduce the basic principles of optics relevant for instrumentation design, outline the key laser technologies and setups, and review the state-of-the-art in laser-based beam instrumentation.