MASC (Manageable and Adaptive Service Compositions)** is a policy-based middleware for monitoring of Web service compositions and their dynamic adaptation to various runtime changes. MASC policies are described in our new WS-Policy extension called WS-Policy4MASC. Compared with recent related works, MASC has several distinctive characteristics, such as coordination of adaptation on the SOAP messaging layer and the business process orchestration layer, use of both technical and business metrics for adaptation decisions, and extending the power and flexibility of the new Microsoft .NET 3.0 platform. In this paper, we focus on MASC support for adaptation to address business exceptions and manage runtime faults. For example, a sub-process (or an activity) can be added, deleted, replaced, skipped, or retried. We have been implementing a MASC proof-of-concept prototype and evaluating it on adaptation scenarios from a stock trading case study. Our performance studies of the prototype indicate that overheads introduced by MASC are acceptable.