On top of being a potential candidate of dark matter, primordial black holes (PBHs) can solve other cosmological and astrophysical puzzles and provide a window to the early universe. In this talk, I will discuss potential gravitational wave signals associated with PBHs and how current and future gravitational wave observations could be used to probe the PBH hypothesis. These signals range from the stochastic gravitational wave background created in the young post inflationary universe when PBHs were formed to the recent mergers of PBH binaries.