Neutron stars are the collapsed cores of some massive stars. They pack roughly the mass of our Sun into a region the size of a city. Neutron stars are believed to form in supernovae such as the one that formed the Crab Nebula. The stars that eventually become neutron stars are thought to start out with about 15 to 30 times the mass of our sun. It appears that for initial masses much less than 15 solar masses the star becomes a white dwarf, whereas for initial masses a lot higher than 30 solar masses a black hole results instead. It is estimated that there are 108 neutron stars in our galaxy. About 1000 of these have actually been observed by astronomers so far. This new book presents recent and important research results in the field.