This chapter introduces the concepts, development history, and applications of multi-agent systems. It also elaborates on fundamental issues encountered in networked multi-agent systems, including transmission delays and losses, random arbitrary deployment, measurement and communication noise, random variations in trajectory length, sensor multiplicative failures, and challenges in obtaining global information. The chapter provides an overview of distributed localization estimation and formation control for multi-agent systems and discusses the current research status in these areas. Additionally, some fundamental knowledge about system stability is introduced to lay the foundation for the subsequent research content.