This book provides essential knowledge and insight into numerical analysis, with an emphasis on developing understanding rather than simply presenting computational recipes. It approaches numerical analysis not only as practical tool for solving applied problems, but also as a rich, challenging and rewarding branch of mathematics. Developed over more than a decade from the author’s lecture notes for the undergraduate course Numerical Analysis taught to international students at Nanjing University of Aeronautics and Astronautics (NUAA) since 2005, this textbook is dedicated to readers with a solid foundation in differential and integral calculus and linear algebra. Equally important, it encourages readers to appreciate how these fundamental tools come to life in solving real-world problems. Written in a clear and self-contained style, the book is designed to be accessible not only to mathematicians, but also to scientists and engineers. It serves as textbook for undergraduate students, while also offering a useful reference for researchers and professionals in engineering and applied sciences.