Publisher Summary This chapter describes the different aspects of special functions. The general form of an ordinary linear differential equation of the second order with variable coefficients may be written for complex variables z and w as w′′ + p(z)w′ +q (z)w = 0. A value z = z0 in the neighborhood of which the coefficients p(z) and q(z) are analytic is called an ordinary point of the differential equation. All other points are called singular points or singularities of the differential equation. The only singular point in the finite part of the complex plane is z = 0. The chapter discusses the determination of the domain of convergence of the power series. A majorizing argument is constructed by replacing every cn by a number Cn such that | cn | ≤ Cn. The point at infinity is an ordinary point of the equation w′′ + p(z)w′ + q(z)w = 0 if 2z−z2p(z) and z4q(z) are analytic in the neighborhood of z = ∞.