Abstract: Active networks are a programmable network and the user can insert customized programs into the switches of the network to perform customized computations on the messages flowing through them. As a novel conception, active network offers changing from carrying bits of traditional networks to a more general computation engine. Active networks challenge the interoperability, security, and scalability of the traditional networks. To compare with traditional network, there are some potential advantages of faster deployment, customization of network services, equipped with new network architectures and protocols, etc.. Active network as a novel network architecture can accelerate the pace of standard of network and improve the performance, flexibility and extensibility of network. Here summarized are the background, architecture, implementation, research issues and current research status and direction of active networks.