The 2009 Symposium on Component-Based Software Engineering (CBSE 2009) was the 12thin a series ofsuccessful eventsthat havegrowninto the main forum for industrial and academic experts to discuss component technology. Component-based software engineering (CBSE) has emerged as the under- ing technology for the assembly of ?exible software systems. In essence, CBSE is about composing computational building blocks to construct larger building blocks that ful?ll client needs. Most software engineers are involved in some form of component-based development. Nonetheless, the implications of CBSE adoption are wide-reaching and its challenges grow in tandem with its uptake, continuing to inspire our scienti?c speculation. Component-based development necessarily involves elements of software - chitecture, modular software design, software veri?cation, testing, con?guration and deployment. This year's submissions represent a cross-section of CBSE - search that touches upon all these aspects. The theoretical foundations of c- ponent speci?cation, composition, analysis, and veri?cation continue to pose research challenges. What exactly constitutes an adequate semantics for c- munication and composition so that bigger things can be built from smaller things? How can formal approaches facilitate predictable assembly through b- ter analysis? We have grouped the proceedings into two sub-themes that deal with these issues: component models and communication and composition. At the same time, the world is changing.

Component Models: Taxonomies and Applications.- On Component Identification Approaches - Classification, State of the Art, and Comparison.- Domain-Specific Software Component Models.- A Model-Driven Engineering Framework for Component Models Interoperability.- Component Integration: Patterns and Profiling.- Process Patterns for Component-Based Software Development.- Selecting Fault Tolerant Styles for Third-Party Components with Model Checking Support.- Extracting Behavior Specification of Components in Legacy Applications.- Towards Dynamic Component Isolation in a Service Oriented Platform.- Communication and Composition.- Control Encapsulation: A Calculus for Exogenous Composition of Software Components.- Component Specification Using Event Classes.- Integrating Functional and Architectural Views of Reactive Systems.- Extra-Functional Analysis.- Integration of Extra-Functional Properties in Component Models.- Modelling Layered Component Execution Environments for Performance Prediction.- Component-Based Real-Time Operating System for Embedded Applications.- Components within the Development Life Cycle.- Services + Components = Data Intensive Scientific Workflow Applications with MeDICi.- Ensuring Consistency between Designs, Documentation, Formal Specifications, and Implementations.- Unit Testing of Software Components with Inter-component Dependencies.