The textbook "Ordinary and Partial Differential Equations" offers a comprehensive introduction to ordinary and partial differential equations, which is relevant for students and educators in the fields of mathematics, physics, and engineering. The authors present the topics through 50 well-established lectures that clearly and precisely explain mathematical concepts. Each chapter includes fully worked-out examples and helpful illustrations that enhance understanding. At the end of the chapters, there are exercises that provide readers with the opportunity to deepen and apply what they have learned. The focus is on application-oriented topics, including the solution of ODEs in the form of power series and the treatment of special functions such as Bessel and hypergeometric functions, as well as orthogonal functions and polynomials. The book assumes a basic knowledge of analysis, making it ideal for anyone looking to engage deeply with differential equations.