This book focuses on the practical aspects of computational electrodynamics. A short review of electromagnetic field theory and an illustrative introduction to basic concepts of numerical methods provide the mathematical and physical background. In the main part the book guides the reader step-by-step through the modeling process: from the initial "what question shall the model answer?", through the setting up of a computer model by creating geometry, boundary conditions, sources, to post processing, validation and optimization. A number of antenna and filter examples demonstrate the advantages and disadvantages of different numerical methods. The book creates a realistic view of the capabilities and limits of up-to-date 3D field simulators and how to apply this knowledge efficiently to EM analysis and design of RF applications in modern communication systems.