Invisible axion search methods

Originally hypothesized to explain the absence of $C\phantom{\rule{0}{0ex}}P$ violation in the strong interactions, the axion has emerged as a candidate constituent of dark matter. This review guides the reader through the search methods for the QCD axion as well as for new kinds of particles with axionlike properties. For each case, the physics of the method, the signatures, and the background are discussed in depth. A must-have addition to the quiver of axion hunters.