No longer a creation of the theoretical physicists' imagination, neutron stars and black holes have been found in abundance in the observed universe and have allowed astrophysicists to push our exploration of basic physics into extreme environments unattainable in the laboratory. Neutron stars exist as radio pulsars that are splendid clocks for testing general relativity and high energy astrophysics. They can spin with almost kHz frequencies and support 100GT magnetic fields. They can be gravitational machines for transforming the rest mass energy of accreting gas into X-rays and can explode to create gamma ray outbursts with millisecond timescales. Black Holes are gravitational collapsed objects that possess event horizons that outgoing matter and radiation cannot cross. They come in two sizes. Star-sized holes are observed when they have binary companions that evolve to supply them with gaseous fuel which can spiral inward towards the event horizon through an "accretion disk". Stellar holes may be formed during special supernova explosions accompanied by gamma ray bursts. Holes as massive as millions to billions of suns reside in the nuclei of most normal galaxies, including our own. When they are supplied with gas they can easily outshine their host galaxies and are then called quasars. When black holes merge, they can create burst of gravitational radiation which may be detectable.