In this talk,we will present a unified framework for handling several cooperative control problems of multi-agent systems such as consensus,formation,flocking,and rendezvous by distributed control laws.Based on the certainty equivalent principle,the distributed control law will be synthesized by combining a purely decentralized control law and a distributed observer.The approach works for linear multi-agent systems and some typical nonlinear multi-agent systems such as multiple Euler-Lagrange systems and multiple rigid-body systems.