Computer simulation has become, alongside experimentation and abstract reasoning, a third major tool of science. The student in the computational sciences needs a background in numerical analysis, and it is one of the objectives of this text to provide that background material. This book covers many of the traditional areas of numerical analysis as well as topics in software development and methods of Monte Carlo simulations. It is designed to serve both as a textbook for a course in numerical methods for students in natural sciences and as a reference for scientists whose research involves numerical computations and simulations. Exercises comprise an important part of the text. The mathematical prerequisites include real analysis and linear algebra, and the text does assume some familiarity with computer programming.