Developing component-based systems supports reuse and modularity but introduces new compatibility problems. Testing and analysis are usually based on the availability of either the source code or the specifications, but COTS components are commonly provided without source code and with incomplete specifications. A dynamic analysis technique called behavior capture and test can reveal COTS component misbehaviors and incompatibilities. BCT first automatically derives behavioral models by monitoring component executions and then dynamically checks these models when the components are replaced or used as part of a new system. Another article related to software composition also appears in this issue ("Open Source Software: All You Do Is Put It Together").