This thesis proposes a new dynamic resource management architecture, Magnet, to meet the requirements of users in flexible and adaptive systems. Computer systems no longer operate in centralized isolated static environments. Technological advances, such as smaller and faster hardware, and higher reliability of networks have resulted in the growth of mobility of computing and the need for run-time reconfigurability. The dynamic management of this diversity of resources is the central issue addressed in this thesis. Applications in environments with frequently changing characteristics are required to participate in dynamic resource management, to adapt to ever-changing conditions, and to express their requirements in terms of quality of service. Magnet enables dynamic trading of resources which can be requested indirectly by the type of service they offer, rather than directly by their name. A dedicated component, the Trader, matches requests for services against demands and establishes a component binding - resource allocation. In addition, the architecture is extensible - it does not constrain the information on services and allows user-customization of the matching process. Consequently, this allows resource definitions to be parametrized (to include QoS-based characteristics), and the matching process to be user-customized (to preform QoS-based negotiation). In order to fulfill the requirements of users relying on ever-changing conditions, Magnet enables runtime adaptation (dynamic rebinding) to changes in the environment, constant monitoring of resources, and scalability of the architecture. The generality of the Magnet architecture is illustrated with several examples of resource allocation in dynamic environments.