Computational fluid dynamics (CFD) is a powerful tool that enables engineers and scientists to simulate fluid flows in a variety of applications, including thermal engineering, biomedical engineering, and environmental modeling. This book provides a comprehensive introduction to CFD, encompassing fundamental theory, mathematical and numerical techniques, and practical applications. The book begins by systematically introducing the basic concepts and terminology of CFD, such as the continuity equation, Navier-Stokes equations, energy equation, source/sink terms, and types of grids. The mathematical and numerical methods utilized to solve the CFD governing equations, including the finite difference method and the finite volume method, are then described in a beginner-friendly manner, accompanied by vivid and straightforward graphical illustrations. In addition to covering the foundation of CFD theory, the book presents several practical applications of CFD in diverse fields such as biomedical modeling, renewable energy, and thermal engineering. To extract useful information, the simulated CFD results need to be analyzed and visualized. Therefore, the book demonstrates common post-processing and visualization techniques, such as contour plots, streamlines, vectors, and charts. Overall, this book provides a comprehensive introduction to CFD, encompassing the essential theory, methods, and applications, making it an ideal choice as a textbook for graduate and post-graduate students or a reference for researchers and engineers working on CFD simulations.