Designed for chemical engineering students and industry professionals, the book shows how to write reusable computer programs by guiding the reader through the process of: establishing the theoretical concept; determining the applicable numerical methods; testing the algorithm through manual calculation; writing and debugging the computer program based on the algorithm; and validating the result, using statistical analysis. All programs in the book are written in the three most popular languages (C, C++, and MATLAB) currently used in the chemical engineering curriculum and in industry. Because the book is written by a chemical engineer, practitioners and students will learn to write programs for appropriate subject matter of interest to them.