Nuclear physics began long before the identification of fundamental particles, with J. J. Thomson's discovery of the electron at the end of the nineteenth century, which implied the existence of a positive charge in the atom to make it neutral. In this Very Short Introduction, Frank Close gives an account of how this area of physics has progressed, including the recognition of how heavy nuclei are built up in the cores of stars and in supernovae, the identification of quarks and gluons, and the development of quantum chromodynamics (QCD). Exploring key concepts such as the stability of different configurations of protons and neutrons in nuclei, Frank Close shows how nuclear physics brings the physics of the stars to Earth and provides us with important applications, particularly in medicine.