Abstract: Cloud computing has been widely adopted by enterprises because of its on-demand and elastic resource usage paradigm. Currently most cloud applications are running on one single cloud. However, more and more applications demand to run across several clouds to satisfy the requirements like best cost efficiency, avoidance of vender lock-in, and geolocation sensitive service. JointCloud computing is a new research initiated by Chinese institutes to address the computing issues concerned with multiple clouds. In JointCloud, users’ diverse and dynamic requirements on cloud resources are satisfied by providing users virtual cloud (VC). A virtual cloud is a special virtualized cloud environment built upon resources from physical cloud vendors such as Amazon, Microsoft and Alibaba. Virtual cloud is in essence a user’s specific cloud working environment having the customized software stacks, configurations and computing resources readily available. Users can develop, test and run tasks in their working environment online through a web browser, without caring about the low-level details like framework installation, configuration and parameter tuning. Such a working environment is built upon a customized VC, which provides the most suitable resources from underlying clouds for the working environment. This environment could span multiple clouds seamlessly, and could help applications elastically scale out to temporarily use new resources from outside parties to deal with peak load problems. The main challenge of virtual cloud is how to dynamically create a VC according to different user’s different requirement and provide application support accordingly. The key to this issue is to build a virtual cloud management system. We have developed a virtual cloud management system prototype named Docklet (https://github.com/unias/docklet). It has been deployed in Peking University serving thousands of students for teaching and exercising purposes (https://iwork.pku.edu.cn).