The growing catalog of gravitational-wave signals from compact object mergers has allowed us to study the properties of black holes and neutron stars more precisely than ever before and has opened a new window through which to probe the earliest moments in our universe's history. Population-level measurements of the masses and spins of compact objects can reveal how these systems form and evolve. Multimessenger observations of compact object mergers can shed light on the properties of the electromagnetic counterparts of these systems, such as short gamma-ray bursts and kilonovae. Finally, observations of the stochastic gravitational-wave background can constrain early-universe physics inaccessible with other means.