The JAMUS platform is dedicated to providing a safe runtime environment for untrusted Java application programs, while offering each of these programs access to the resources it needs to use at runtime. To achieve this goal, JAMUS implements a contractual approach of resource utilisation and control, together with a reservation-based resource management scheme, and a monitoring model. When getting deployed on the platform, a candidate program must first subscribe a contract with the resource manager of the platform. This contract describes the resources the program requires to be able to access at runtime, and how it plans to behave when accessing these resources. Based on this information, the platform can monitor programs at runtime, so that any violation of the contracts they subscribed can be detected and sanctioned. Moreover, since the specific needs of a program are liable to change (or to be refined) dynamically while this program is running, any program hosted by the platform can ask that its contract be re-negotiated at any time.