The spatially distributed structure of complex systems motivates the idea of distributed control. In a distributed control system, the subsystems are controlled by local controllers through information exchange with neighboring agents for coordination purposes. One of the major difficulties of distributed control is due to the complex characteristics such as nonlinearity, dimensionality, uncertainty, and information constraints. This chapter introduces small-gain methods for distributed control of nonlinear systems. In particular, a cyclic-small-gain result in digraphs is presented as an extension of the standard nonlinear small-gain theorem. It is shown that the new result is extremely useful for distributed control of nonlinear systems. Specifically, this chapter first gives a cyclic-small-gain design for distributed outputfeedback control of nonlinear systems. Then, an application to formation control problem of nonholonomic mobile robots with a fixed information exchange topology is presented.