Traditionally an execution environment faces a trade-off between providing high-level or low-level concurrency mechanisms. The former trades flexibility for ease-of-use, while the latter results in a concurrency management closer to applications needs at the cost of an increase in the complexity of the applications code. Thus, one way or another, an application programmer has to match his application’s semantic to the set of abstractions exported by the target execution environment. Most execution environments, such as Java or Corba, are still rigid and closed and thus export high-level and general purpose abstractions that prevent application programmers from having any control or knowledge on the way their applications behave. Because concurrency concerns are closely related to applications semantics, a “one-size-fits-all” approach does hardly work. Hence, we propose a flexible and minimal execution environment 1 that allows dynamic construction of dedicated execution environments and dynamic reconfiguration at both the execution environment and the application level. We present its architecture and its utilization to construct a dynamically adaptable Java runtime that exploits this flexibility to overcome some limitations of traditional Java environments.