Eco4Cloud offers a novel and decentralized solution to modernize the data centers and exploit the potentialities of Cloud Computing, in order to obtain higher efficiency, guarantees of high quality of service for the applications executed in the data centers, and significant energy savings. Eco4Cloud uses the Virtualization technique: the application are hosted by Virtual Machines, VMs, which are allocated and executed on physical machines, or servers. By consolidating the VMs on a number of servers as low as possible, it is possible to power off the remaining servers, or switch them to a low power state, in this way reducing the amount of consumed electrical energy. Moreover, the Eco4Cloud solution prevents possible overload situations, which could deteriorate the quality of service experienced by users. Finally, thanks to the decentralized management, it is possible to reduce the burden related to the administration and monitoring of the data center.