SummaryThis paper characterizes a unified consensus region for multi-agent systems, where there exist fixed physical connections with information exchange. The notions of synchronization region in complex networks and consensus region in multi-agent systems can be explained under this unified framework. The effect of the coupling terms on the consensus regions in different situations is analyzed specifically. Furthermore, necessary and sufficient conditions for consensus of agents under both distributed state feedback and observer-based output feedback control are established. On the basis of a parameter-dependent Lyapunov function, a 2-step controller design procedure is proposed, which can reduce the conservativeness to some extent in comparison with the conventional direct Lyapunov method. In addition, for the case with disturbance, the robustness of the system is investigated. Finally, some numerical examples are presented to illustrate the theoretical results.