  Angular momentum plays a central role in a multitude of phenomena in quantum
mechanics, recurring in every length scale from the microscopic interactions of
light and matter to the macroscopic behavior of superfluids. Vortex beams,
carrying intrinsic orbital angular momentum (OAM), are now regularly generated
with elementary particles such as photons and electrons, and harnessed for
numerous applications including microscopy and communication. Untapped
possibilities remain hidden in vortices of non-elementary particles, as their
composite structure can lead to coupling of OAM with internal degrees of
freedom. However, thus far, the creation of a vortex beam of a non-elementary
particle has never been demonstrated experimentally. We present the first
vortex beams of atoms and molecules, formed by diffracting supersonic beams of
helium atoms and dimers, respectively, off binary masks made from transmission
gratings. By achieving large particle coherence lengths and nanometric grating
features, we observe a series of vortex rings corresponding to different OAM
states in the accumulated images of particles impacting a detector. This method
is general and can be applied to most atomic and molecular gases. Our results
may open new frontiers in atomic physics, utilizing the additional degree of
freedom of OAM to probe collisions and alter fundamental interactions.
