The Dirac equation was formulated by Paul Dirac in 1929, and ever since then it has played an important role in several areas of physics and mathematics and has plenty of applications in quantum mechanics. The equation describes the relativistic spin-1/2 particles, such as, electrons or positrons, which move in different electric and magnetic fields. In this book, some topics concerning the Dirac equation are studied. Since the self-adjointness of operators is a fundamental information in quantum mechanics, several self-adjoint extensions of the Dirac operator coupled to electromagnetic...