Many existing management systems are not evolutive or adaptive, leading to multiplicity over time and increasing the management burden. Policy-based management approaches may assist in making networks less complex and more automated, but to date they have not yet been able to evolve to support new service sets or provide the capacity for differentiation.We present the architecture for a policy-based system named Pronto that helps to deal with these issues. Layered network and service models are built above an extensible virtual device model that supports heterogenous management interfaces. Interchangeable management components provide the basic building blocks to construct logical services. The integrated policy-driven service definition language automates the management of the services in a manner that is adaptive, dynamic and reactive to improve the user's overall service experience.