Book excerpt: The LNCS Journal Transactions on Aspect-Oriented Software Development is devoted to all facets of aspect-oriented software development (AOSD) techniques in the context of all phases of the software life cycle, from requirements and design to implementation, maintenance and evolution. The focus of the journal is on approaches for systematic identification, modularization, representation and composition of crosscutting concerns, i.e., the aspects and evaluation of such approaches and their impact on improving quality attributes of software systems. This volume, the fourth in the Transactions on Aspect-Oriented Software Development series, presents 5 revised papers together with 2 guest editors' introductions. The papers, which focus on mapping of early aspects across the software lifecycle, and aspects and software evolution, have passed through a careful peer reviewing process, carried out by the journal's Editorial Board and expert referees.