This paper presents an overview of the theory and known techniques for multi-cell MIMO (multiple input multiple output) cooperation in wireless networks. In dense networks where interference is the key capacity-limiting factor, multi-cell cooperation can significantly improve system performance. The paper explores multi-cell MIMO cooperation from various perspectives, including fundamental information-theoretic limits, coding and signal processing developments, and practical issues like scalability and system-level integration. It also suggests promising research directions. The paper discusses two basic scenarios for cooperation in wireless networks: a virtual MIMO model for cooperative transmission over interfering links and relay-based cooperation. Conventional diversity and relaying schemes improve link-level performance but do not address severe inter-cell interference. Instead, the paper advocates for using "virtual" or "network" MIMO to maximize co-channel links with acceptable quality of service. In the high SNR regime, this corresponds to the multiplexing gain of the network, or the number of degrees of freedom. Relay-based cooperative techniques mitigate propagation conditions by allowing communication via a third party. Amplify-forward, decode-forward, and compress-forward schemes exploit relay nodes to provide extra diversity. Conventional non-cooperative approaches to interference, such as spatial reuse partitioning, prevent spectral resource reuse but result in severe interference at the cell edge. In contrast, the emerging view on network design advocates proactive interference management through coordination. The paper discusses the challenges of multi-cell MIMO systems, including understanding information-theoretic capacity, algorithm development for precoding and decoding, and the equivalence between multi-cell and MIMO systems under ideal backhaul conditions. It also addresses practical issues like imperfect synchronization, channel estimation, and network latency. The paper outlines the scope and organization of the paper, focusing on the adaptation of multi-antenna processing principles to multi-cell cooperation. It reviews key information-theoretic results, the design of practical MCP techniques, and the feasibility of scalable and distributed MIMO cooperation. It also addresses system-level implementation issues and provides perspectives on promising research avenues. The paper models multi-cell cooperation, discusses different levels of cooperation, and presents capacity results for multi-cell MIMO cooperation. It reviews the linear Wyner model, discusses the impact of cooperation on cellular systems, and presents capacity results for the Wyner uplink model. It also considers limited backhaul to the CP and local BS backhaul, discussing the implications of finite-capacity backhaul links on system performance. The paper concludes with a discussion of the implications of these findings for future research and practical implementation.This paper presents an overview of the theory and known techniques for multi-cell MIMO (multiple input multiple output) cooperation in wireless networks. In dense networks where interference is the key capacity-limiting factor, multi-cell cooperation can significantly improve system performance. The paper explores multi-cell MIMO cooperation from various perspectives, including fundamental information-theoretic limits, coding and signal processing developments, and practical issues like scalability and system-level integration. It also suggests promising research directions. The paper discusses two basic scenarios for cooperation in wireless networks: a virtual MIMO model for cooperative transmission over interfering links and relay-based cooperation. Conventional diversity and relaying schemes improve link-level performance but do not address severe inter-cell interference. Instead, the paper advocates for using "virtual" or "network" MIMO to maximize co-channel links with acceptable quality of service. In the high SNR regime, this corresponds to the multiplexing gain of the network, or the number of degrees of freedom. Relay-based cooperative techniques mitigate propagation conditions by allowing communication via a third party. Amplify-forward, decode-forward, and compress-forward schemes exploit relay nodes to provide extra diversity. Conventional non-cooperative approaches to interference, such as spatial reuse partitioning, prevent spectral resource reuse but result in severe interference at the cell edge. In contrast, the emerging view on network design advocates proactive interference management through coordination. The paper discusses the challenges of multi-cell MIMO systems, including understanding information-theoretic capacity, algorithm development for precoding and decoding, and the equivalence between multi-cell and MIMO systems under ideal backhaul conditions. It also addresses practical issues like imperfect synchronization, channel estimation, and network latency. The paper outlines the scope and organization of the paper, focusing on the adaptation of multi-antenna processing principles to multi-cell cooperation. It reviews key information-theoretic results, the design of practical MCP techniques, and the feasibility of scalable and distributed MIMO cooperation. It also addresses system-level implementation issues and provides perspectives on promising research avenues. The paper models multi-cell cooperation, discusses different levels of cooperation, and presents capacity results for multi-cell MIMO cooperation. It reviews the linear Wyner model, discusses the impact of cooperation on cellular systems, and presents capacity results for the Wyner uplink model. It also considers limited backhaul to the CP and local BS backhaul, discussing the implications of finite-capacity backhaul links on system performance. The paper concludes with a discussion of the implications of these findings for future research and practical implementation.