The event-triggered communication is introduced in Chap. 7 as a means of reducing the communication resources required by multiple UAVs. Furthermore, communication interactions between UAVs can be reduced by switching between connected and unconnected topologies, thus reducing the wastage of communication resources. Nevertheless, communication topology switching gives rise to topology and controller switching that occur in a nonsynchronous manner, which is to say, asynchronous switching. In order to address this problem, an asynchronous switching observer is proposed in this chapter, which ensures that the follower UAVs are able to estimate the leader UAV state information under topology switching.