Today, we experience an unprecedented integration of previously disconnected systems. Consequently, there is a leap in the complexity of the software controlling these systems. The challenge we are facing is how to master this complexity while at the same time increasing the reliability of programs. A key element for tackling that challenge will be a better understanding of software composition. Good techniques for software composition are the keys to scalable systems. The principal means of writing and composing software is a programming language. Consequently, advances in programming language design are an important factor in solutions of the software composition problem. This is what we work on in our group.