Pulsars are extraordinarily rich natural laboratories that are being used by astronomers to innovatively explore the fundamental physics of extreme states of matter, probe the regime of strong gravity, precisely test the predictions of Einstein's theory of general relativity, and much more. Pulsars are neutron stars, exotic astronomical objects that are one of the possible endpoints of stellar evolution for stars more massive than the Sun. First discovered in 1967, pulsars are very dense stellar objects that rotate up to 750 times per second, are about 20 kilometers in diameter, and emit narrow, lighthouse-like beams of radiation that can be observed by radio telescopes if their beams sweep through the line-of-sight to the Earth. The relatively rare and very fast “millisecond pulsars” may provide an opportunity to directly detect gravitational waves from the near and distant universe and inaugurate the field of gravitational wave astronomy. An international team of astronomers is now building a precision, galactic-scale gravitational wave detector that observes a sample of millisecond pulsars and times their individual pulses with a precision of tens to hundreds of nanoseconds.