This book provides students with solid knowledge of the basic principles of differential equations and a clear understanding of the various ways of obtaining their solutions by applying suitable methods. It is primarily intended to serve as a textbook for undergraduate students of mathematics. It will also be useful for undergraduate engineering students of all disciplines as part of their course in engineering mathematics. No book on differential equations is complete without a treatment of special functions and special equations. A chapter in this book has been devoted to the detailed study of special functions such as the gamma function, beta function, hypergeometric function, and Bessel function, as well as special equations such as the Legendre equation, Chebyshev equation, Hermite equation, and Laguerre equation. The general properties of various orthogonal polynomials such as Legendre, Chebyshev, Hermite, and Laguerre have also been covered. A large number of solved examples as well as exercises at the end of many chapter sections help to comprehend as well as to strengthen the grasp of the underlying concepts and principles of the subject. The answers to all the exercises are provided at the end of the book