The chapter discusses the concept of software agents and their role in facilitating interoperability among diverse software programs. It highlights the challenges posed by heterogeneity and dynamics in the software environment, such as different programming languages and frequent rewrites of programs. Agent-based software engineering is introduced as a solution, where application programs are designed as software agents that communicate with peers using a common, expressive agent communication language (ACL). ACL is described in detail, including its vocabulary, inner language KIF (Knowledge Interchange Format), and outer language KQML (Knowledge Query and Manipulation Language). The chapter also explores the behavioral constraints of agents, such as veracity, autonomy, and commitment, and discusses methods for converting legacy software into agent-based systems. Finally, it outlines the architecture of multiagent systems, including direct communication and assisted coordination approaches, and the role of facilitators in enabling interoperation. The authors conclude by emphasizing the potential of agent technology to achieve seamless interoperability across systems.The chapter discusses the concept of software agents and their role in facilitating interoperability among diverse software programs. It highlights the challenges posed by heterogeneity and dynamics in the software environment, such as different programming languages and frequent rewrites of programs. Agent-based software engineering is introduced as a solution, where application programs are designed as software agents that communicate with peers using a common, expressive agent communication language (ACL). ACL is described in detail, including its vocabulary, inner language KIF (Knowledge Interchange Format), and outer language KQML (Knowledge Query and Manipulation Language). The chapter also explores the behavioral constraints of agents, such as veracity, autonomy, and commitment, and discusses methods for converting legacy software into agent-based systems. Finally, it outlines the architecture of multiagent systems, including direct communication and assisted coordination approaches, and the role of facilitators in enabling interoperation. The authors conclude by emphasizing the potential of agent technology to achieve seamless interoperability across systems.