This book presents an introduction to the principles of the fast Fourier transform. The book covers FFTs, frequency domain filtering, and applications to video and audio signal processing. It feeds the demand for an updated book reflecting the various developments in FFT and its applications, and it fills the need from instructors and students for a book dealing with the latest FFT topics. It also has adopted modern approaches like MATLAB examples and projects for better understanding of diverse FFTs. The emphasis of the book is on the foundation of FFTs such as the decimation-in-time FFT, decimation-in-frequency FFT algorithms, integer FFT, prime factor DFT and so on. It includes references to books, review papers, lists of applications, hardware/software, and useful websites.