Beyond-3G (B3G) systems have been envisaged as an evolution and convergence of mobile/wireless communication systems and IP technologies to offer a multitude of services over a variety of access technologies. To fulfill the vision, it is necessary to understand the requirements with respect to the support of heterogeneity in network accesses, communication services, mobility, user devices, and so on. Besides, it is equally important to promote the necessary research in networking technology by providing a guiding framework of research areas and technical issues with priority. The new architectures and technologies have to address the fundamental assumptions and requirements that govern the design. All these issues are being tackled by the cooperative network group (CoNet) of WWRF; the group is working on a series of white papers outlining B3G visions and roadmap, architectural principles, research challenges, and candidate approaches. This article outlines the CoNet concept, architectural principles, and guidelines for research into cooperative networks assuming that the B3G systems are built over generic IP networking technologies. The article also presents the key research challenges, research framework, and major network components and technologies. The key points are that the system should be layered on demand, encourage reuse if independent modularized functional blocks, support multiple services and service creation, ensure consistent end-to-end connectivity across different access technologies, and cooperate in terms of network control, operations, and maintenance. The architecture includes the endpoints of communications as part of the communications system, and provides a secure and trusted environment in which network functions are performed; the network should self-organize dynamically. Additionally, the article presents the IST WSI architecture proposed to CoNet as reference model along with some approaches to the outlined research challenges. Finally, this study selects three important network components and technologies (i.e., mobility management, multiple access, and moving networks) in order to provide with answers and possible solutions the research challenges presented in earlier sections.