The use of third-party components is helpful while writing complex software systems, but it can be difficult to debug software that interacts with third-party components. To address this problem, a mechanism for determining if one is using the component correctly would be beneficial. Reading component documentation may or may not help, depending on its clarity and precision. A formally specified contract for that component would be better, and would also allow run-time contract verification via assertions. The client of the component could enable these assertions during development and debugging, and then disable them for the final production release to increase performance. This thesis presents nContract, a tool that provides configurable run-time contract verification without requiring component recompilation or source code access. nContract allows component developers to formally specify .NET components using attributes. This contract information is retrieved from the compiled component's metadata and a subclass is generated for each formally specified type. All members of the component's interface are overridden and contract assertions are wrapped around calls to the base class. As long as the component client uses a factory to create instances of the component's types, the decision of whether or not to create assertion-checked or unchecked objects can be deferred until run-time. / Master of Science