Abstract: Axions and other hypothetical Weakly Interacting Slim Particles (WISPs) might explain open questions in elementary particle physics and simultaneously constitute the dark matter in the universe. Second and third generation experiments are being prepared to search for such WISPs. Any detection would give insight into particle physics well beyond the energy scales reachable with present or future accelerators. This colloquium will summarize the physics case for WISPs, the present experimental achievements, and the bright perspectives of forthcoming detectors. Some emphasis will be put on the ALPS II experiment at DESY, which combines particle physics know-how with optics expertise from gravitational wave interferometers.