This paper describes a model driven development approach for software product lines based on Web services, in which feature selection drives the dynamic customization of the product line architecture and implementation to derive the application. During product line modeling, feature and their dependencies are described in a feature model. The product line architecture is based around a client/server pattern consisting of user interface objects interacting with Web services. During application engineering, features are selected by the application engineer and used to dynamically customize the product line architecture and implementation.