This book introduces the time domain numerical methods to solve electromagnetic problems, including finite-difference time-domain (FDTD) method, the finite element method (FEM) and method of moment (MOM). It also presents emerging methods in the recent ten years for electromagnetics simulations. All these methods can be unified under a single mathematic framework. This is one of the few books to unify and compare different time-domain methods and clarify their respective advantages and disadvantages.