Differential equations find its applications in all fields of science and engineering because it can describe the modeling of nearly all systems involving rate of change. Due to this fact, it has widespread use in physics, engineering, economics, social science and also in biology. Many systems involving differential equations are so complex, or the systems they describe are so large, that a purely mathematical analysis is not possible and it provides only the existence of the solution, therefore, we have to seek the approximate solution by means of the numerical methods. Hence in these types of complex systems, the computer simulations and numerical approximations are useful. The techniques for solving differential equations based on the numerical approximations can be used to handle the complex systems of differential equations on a common PC now-a-days. This is the first book in which the numerical solution procedures of six important methods are given for all the three types of the boundary conditions with programs in C.