  Gravitational waves from inspiraling sub-solar mass compact objects would
provide almost definitive evidence for the existence of primordial black holes.
In this chapter, we explain why these exotic objects are interesting candidates
for current and future gravitational-wave observatories, and provide detailed
explanations of how they are searched for. We describe one method, matched
filtering, to search for binaries with masses between $[0.01,1]M_\odot$.
Furthermore, since signals from inspiraling planetary- and asteroid-mass mass
compact binaries ($[10^{-9},10^{-2}]M_\odot$) would spend hours to years in the
detector frequency band, we explain the novel pattern recognition techniques
that have been developed to search for them. Finally, we describe extreme mass
ratio inspiral (EMRI) systems, and how these will be searched for in future
space-based detectors. For all mass regimes, we comment on the prospects for
detection.
