Nature: For almost a century, physicists have had in hand “the” theoretical framework of the known world—quantum mechanics. But whereas the world clearly comprises large complex systems, quantum mechanics is usually associated with the microworld of atoms and elementary particles, and is hardly ever considered as an underlying feature in our daily life.This is even more pronounced for some of the seemingly weird predictions of quantum mechanics, such as entanglement, which asserts that the quantum state of physically separated objects is mutually and inextricably connected. J. D. Jost and colleagues in Nature demonstrate quantum entanglement of two spatially separated mechanical oscillators. Although the quantum nature of mechanical oscillators has been known and observed for a long time, the entanglement of their oscillating motions has not, and its demonstration adds a valuable tool to the toolbox of quantum-state engineering. Related LinksEntangled mechanical oscillators