Since the success of Amazon’s Elastic Compute Cloud (a.k.a. EC2), the concept of cloud computing has been quickly adapted worldwide, from major content providers (such as Google and Microsoft), solution providers to small business enterprise. In contrast to traditional Internet services, cloud computing provides not only storage capacity, but also computing powers. It allows end-users to access data from anywhere at anytime. It equips enterprises with ITsolutions at low cost. Such computing services are supported by large data and processing centers that may or may not located at the same location. Despite the massive computing power, storage capacity and great flexibility, cloud computing is facing challenges in sustainability, privacy, security, robustness, data migration, throughput, and many more. Harnessing all the distributed storage and power together in a seamless architecture is also a great challenge. To address these, peer-to-peer (P2P) techniques have been proposed, e.g., in data centers, at the core as overlay network, and at the edge of the cloud, so that cloud services can be provided in the most effective manner. The goal of this special issue is to foster and exchange ideas on innovative work for P2P cloud computing. It has been successful in attracting many high-quality submissions in the areas of novel P2P or overlay technology for cloud computing, P2P solutions for storage and data migration, green computing and energy efficiency, and overlay and P2P techniques to support Internet and mobile streaming cloud, economics and management issues in P2P cloud systems, etc. After a rigorous review process, we have carefully selected five papers, covering a rather wide spectrum related to the area of P2P cloud systems. The paper “Cost and Profit Driven Cloud-P2P Interaction”, authored by Jacob Chakareski, proposes a utility-driven scheduling strategy to improve video quality, and to reduce frame-freeze frequency and play-out latency in a video streaming system. In contrast to existing proposal, the new strategy takes advantages of both the cloud and P2P infrastructures. On one hand, the cloud is used manage P2P systems, especially in discovering neighbors. On the other hand, peers are awarded by the cloud for their contributions in assisting other peers. In addition to analytical study, the author also provides simulation results to support the claims The paper “Liquidstream II Scalable P2P Overlay Optimization with Adaptive Minimal Server Assistance for Stable and Efficient Video On Demand”, authored by Konstantinos Deltouzos, IliasGkortsilas, Nikolaos Efthymiopoulos, and Spyros Denazis, proposes a Video on Demand system based on scalable P2P network. With the focus on design of Liquidstream II, the paper addresses challenging issues in seeking an effective P2P method for optimizing video communication process. The discussions include distributed and effective peer discovery mechanisms, optimization mechanisms for P2P overlay, and methods for invoking distributed media servers with minimum server assistance. In addition to mathematical analysis, the authors also provide a significant amount of simulation results to support the studies. S.<H. G. Chan The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon Hong Kong, China e-mail: gchan@cse.ust.hk