Optomechanics is a quickly evolving research field investigating systems where light is coupled to mechanical degrees of freedom of micro- and nanostructures. Artificially designing such structures gives rise to applications in extremely sensitive sensing devices and quantum information processing. On the other hand, such systems can be used as models in the examination of solid state and open quantum systems, as well as foundational questions in quantum mechanics. This graduate textbook gives a coherent overview of the field, including background knowledge on open quantum systems and nanophotonics. The author team -- consisting of a theoretic and and experimental physicist -- then discusses a multi-faceted overview of principles and effects arising from optical forces and cooling in such systems including theoretical perspectives, experimental techniques, actual implementations, as well as design, simulation, and manufacturing issues.