This forward-thinking book presents the finite-difference frequency-domain (FDFD) method. FDFD is the frequency-domain relative of the finite-difference time-domain (FDTD) method used for simulating electromagnetic and photonic devices. Special techniques in MATLAB are presented that will allow readers to write their own FDFD programs, as well as review key concepts in electromagnetics. Guided modes in waveguides, photonic band diagrams, and isofrequency contours of periodic structures are explored. Readers learn how to simulate waves through diffraction gratings, beams through photonic crystals, and optical integrated circuits, as well as how to modify FDFD to easily perform parameter sweeps, such as plotting reflection and transmission through a device as a function of frequency. The book includes all of the required MATLAB codes and a detailed explanation of the programs to explain how to simulate devices in the real world.