The consensus problem in a multi-agent system with general nonlinear coupling is investigated in this paper. It is demonstrated that, under suitable conditions on communication all agents approach, a prescribed value if a small fraction of them are controlled by simple feedback control. The stability analysis is based on a blend of graph-theoretic and system-theoretic tools where the contraction analysis and multiple Lyapunov functions play central roles. Numerous numerical examples, which support the analytical results very well, are also included. (C) 2009 Elsevier Ltd. All rights reserved.