On 16 May, a workshop on "Digital Twins" took place at Middlesex University in London - with participants from the fields of computer science, medicine and engineering. Ulrich Frank gave a presentation entitled "Digital Twins: a Case for (Multi-Level) Modelling". Against the background of a critical analysis of the current hype, he presented opportunities and challenges for research. He also outlined the potential that multi-level language architectures offer for the development of highly integrated systems of systems.