As Internet services grow in complexity, Internet Service Providers (ISPs) are finding out that the ad hoc methods that they have employed thus far to monitor and diagnose their services are not sufficient to provide acceptable service quality to their subscribers. In this paper, we demonstrate how service models can he used by ISPs to effectively manage their service offerings. A service model encapsulates a human expert's knowledge of a service, its components, and its interdependencies with other services. In addition, using ongoing measurements, a service model tracks the health of the different services and their components. By traversing a service model top-down, an operator can not only assess the overall health of a service, but also easily correlate the health of all the services and service components to determine the root cause of any problems that may occur. By minimizing the time and effort needed to diagnose problems, service models enable ISP operators to efficiently resolve problems that occur in an ISP environment. Since each ISP system is unique in many respects, unique service models have to be crafted for each of the services in every ISP system. Handcrafting customized service models requires enormous effort and time on the part of a human expert, a luxury that few ISPs can afford. In this paper, we describe a methodology for constructing customized service models for a target ISP system with minimal human intervention. This methodology relies on a service model creation engine that composes a custom service model for an ISP system using a predefined service model template specification and automatically discovered information about the target ISP system. We describe a prototype implementation of this methodology and present an example of a service model obtained from a real-world ISP system. The concepts described are applicable for the management of networks and services in enterprise systems as well.