Star clusters as gravitational wave factories

Stellar-mass black hole candidates have been reported in several star clusters, based on accretion signals or radial velocity variations of companion stars. These individual black holes probably represent much more abundant populations of black holes. I present comparisons of dynamical cluster models to observations of various star clusters that support the idea that black hole populations in clusters are a common phenomenon. I then show how black holes in star clusters contribute to the rapidly growing number of gravitational wave detections through the dynamical formation of binary black holes.