This paper presents an agent-based architecture for optimally managing resources in distributed environments. The agent-based approach allows for maximal autonomy in agent negotiation and decision-making. A three-layer agency-based architecture is proposed, consisting of the user, agency and application domain layers. Agencies correspond to enterprise functional units, and agents are associated with agencies. A formal model of resources and constraints is presented, and it is shown that, under certain assumptions, optimal resource decompositions and allocations can be achieved. A distributed protocol is developed for agencies and agents to negotiate and exchange resources autonomously, while still satisfying both local and global constraints.