This book comprehensively and systematically elaborates on the theory, methods, and applications of multirate signal processing. It comprises 12 chapters in total. Chapters 1-4 introduce foundational theories, mainly including basic concepts of sample rate conversion, network structure and efficient implementation of multirate systems, two-channel filter banks, and channel-free filter banks. Chapters 5-8 explain extended theories, discussing wavelet transform and filter banks, fractional domain multirate signal processing, multi-dimensional multirate signal processing, multi-scale directional transforms, and directional filter banks. Chapters 9-12 are the application part, focusing on the use of multirate techniques in MATLAB, the application of filter banks in digital communication, the utilization of filter banks in audio coding, and the application of wavelet transform in image processing.