In this chapter, we view the development and maintenance of high-quality electronic commerce (ecommerce) applications from a Web engineering perspective. A methodology for deploying patterns as means for improving the quality of e-commerce applications is presented. To that regard, relevant quality attributes and corresponding stakeholder types for the e-commerce applications are identified. The role of development process, the challenges in making optimal use of patterns, and feasibility issues involved in doing so, are analyzed. The activities of a systematic selection and application of patterns are explored. Examples illustrating the use of patterns during macro- and micro-architecture design of business-to-consumer (B2C) e-commerce applications are given. The implications of the use of patterns in a Semantic Web context are briefly highlighted.