Multistage interconnection networks (MINs) can be designed for parallel computing and switching fabrics. Multistage sorting networks can be one of the many applications using interconnection networks. In this monograph, the generalized odd-even merge design is discussed in detail. Designing switching network is another important application of the multistage networks. Generally, interconnection network can be blocking, rearrangeably nonblocking, or nonblocking, or with variable connecting capabilities, from rearrangeable for permutation to nonblocking for multicast services. Novel multistage switching fabric designs, the PINIUM and PINIUM+ switches, for packet switching and multicasting are discussed. A novel switching framework of high-performance hardware schedulers for various buffering techniques based on interconnection networks are discussed.