Lessons Learned From Microkernel Verification Bernhard Beckert and Thorsten Bormer Software verification tools have become a lot more powerful in recent years. Even verification of large, complex systems seems feasible, as demonstrated in the L4.verified and Verisoft XT projects. Still, functional verification of large software systems is rare. In this paper we hint at some issues that may impede widespread introduction of formal verification in the software lifecycle process.