I am an associate professor in the School of Computer Science at Carnegie Mellon University, interested in limits of modularity and complexity caused by variability in software systems. I develop mechanisms, languages, and tools to implement variability in a disciplined way despite imperfect modularity, to understand feature interactions and interoperability issues, to detect errors, to help with nonmodular changes, and to improve program comprehension in software systems, typically systems with a high amount of variability. Among others, I have developed approaches to parse and type check all compile-time configurations of the Linux kernel in the TypeChef project.