Architectural knowledge has been recognized by the software architecture community as a self-contained research area in software architecture, and brought along some promising research directions. In this workshop we discuss the issues that lead to the application of architectural knowledge in research and industrial practice, ongoing research and new ideas to advance the field. In its previous editions this workshop examined the state of the art and practice, future challenges and trends, and architectural knowledge as perceived by different research communities, including requirements engineering, service-oriented computing and international standardization. This fourth edition will discuss, among others, the application, experimentation, specialization and use of architectural knowledge theory and approaches.