With the rapid development of sensing, information processing, and communication technologies, the research in the emerging area of networked control systems (NCSs) has attracted considerable attention in the research community. The purpose of this survey is to provide a review of the state-of-the-art of such research. We particularly discuss various network conditions required for different control purposes, such as the minimum rate coding for stabilizability of linear systems in the presence of time-varying channel capacity, the critical packet loss condition for stability of the Kalman filter with intermittent observations, network topology for coordination of networked multi-agent systems, as well as event-based sampling for energy and communication efficiency. The common goal of discussion on these topics is to reveal the effect of the communication network on the operation of the networked systems.