Although most of research efforts are made on single-channel wireless networks, multichannel environment already exists in real-world systems. In this chapter, we survey current research works in multichannel wireless networks, especially in multihop wireless networks, such as wireless ad hoc, sensor, and mesh networks. We will focus on those optimization issues, to explore the hardness of extensions from single channel to multichannel and valuable research topics. The chapter is divided into four parts: (1) introduction, (2) multi-interface assignment, (3) channel assignment, and (4) network routing. For each part, we give a detail explanation of the latest research in multichannel wireless networks.