With industrial development and the expansion of oil pollution, the problem of water pollution has been intensified and the separation of oil from oily water is an important pursuit. In this chapter, we have considered the understanding and general approaches to superhydrophobic surfaces and their application in various oil–water separations, including oil-in-water and water-in-oil emulsions. However, the chapter is not only limited to superhydrophobic surfaces but is also extended to other superwettable surfaces. The classification of oil–water separations and corresponding optimal design in theory are also conducted. Some challenges and potential promising breakthroughs are also included.