It is our great pleasure to host the fourth edition of the Domain-Specific Aspect Languages workshop (DSAL09), as part of the eight International Conference on Aspect-Oriented Software Development (AOSD09). The tendency to raise the abstraction level in programming languages towards a particular domain is also a major driving force in the research domain of aspect-oriented programming languages. The DSAL workshop series aims to bring the research communities of domain-specific language engineering and domain-specific aspect design together. In the editions held at GPCE06/OOPSLA06 and AOSD07 we approached domain-specific aspect languages both from a design and a language implementation point of view. At AOSD08 we explicitly invited contributions of work on adding domain-specific extensions (DSXs) to general-purpose aspect languages (GPALs). We continue this trend for this edition as the focus on language embedding raises specific issues for language designers, such as proper symbiosis between, and composition of, DSXs.