This paper has reviewed the main concepts and issues associated with the theory and practice of intelligent agents. It has drawn together a very wide range of material, and has hopefully provided an insight into what an agent is, how the notion of an agent can be formalised, how appropriate agent architectures can be designed and implemented, how agents can be programmed, and the types of applications for which agent-based solutions have been proposed. The subject matter of this review is important because it is increasingly felt, both within academia and industry, that intelligent agents will be a key technology as computing systems become ever more distributed, interconnected, and open. In such environments, the ability of agents to autonomously plan and pursue their actions and goals, to cooperate, coordinate, and negotiate with others, and to respond flexibly and intelligently to dynamic and unpredictable situations will lead to significant improvements in the quality and sophistication of the software systems that can be conceived and implemented, and the application areas and problems which can be addressed.