The increasing needs for computing power have led to parallel and distributed computing, which harness the power of large computing infrastructures in a concurrent manner. Recently, virtualization technologies have increased in popularity, thanks to hypervisors improvements, the shift to multi-core architectures, and the spread of Internet services. This has led to the emergence of cloud computing, a paradigm offering computing resources in an elastic, on-demand approach while charging only for consumed resources. In this context, this thesis proposes four contributions to leverage the power of multiple clouds. They follow two directions: the creation of elastic execution platforms on top of federated clouds, and inter-cloud live migration ...