Small things are quantum and big things are classical. But where is the boundary between the two regimes and what happens there? Once the preserve ofgedankenexperiments, such questions are increasingly tackled in the lab. Markus Arndt, Anton Zeilinger, and their colleagues at the University of Vienna explore the quantum‐classical boundary by subjecting ever larger molecules to matter interferometry. Their latest experiment, on hotC70buckyballs, supports the emerging consensus that an object's interaction with the environment, rather than its mere size or even its complexity, dictates its classicality.