  Since its first isolation in 2004, graphene has been found to host a plethora
of unusual electronic transport phenomena, making it a fascinating system for
fundamental studies in condensed-matter physics as well as offering tremendous
opportunities for future electronic and sensing devices. However, to fully
realise these goals a major challenge is the ability to non-invasively image
charge currents in monolayer graphene structures and devices. Typically,
electronic transport in graphene has been investigated via resistivity
measurements, however, such measurements are generally blind to spatial
information critical to observing and studying landmark transport phenomena
such as electron guiding and focusing, topological currents and viscous
electron backflow in real space, and in realistic imperfect devices. Here we
bring quantum imaging to bear on the problem and demonstrate high-resolution
imaging of current flow in graphene structures. Our method utilises an
engineered array of near-surface, atomic-sized quantum sensors in diamond, to
map the vector magnetic field and reconstruct the vector current density over
graphene geometries of varying complexity, from mono-ribbons to junctions, with
spatial resolution at the diffraction limit and a projected sensitivity to
currents as small as 1 {\mu}A. The measured current maps reveal strong spatial
variations corresponding to physical defects at the sub-{\mu}m scale. The
demonstrated method opens up an important new avenue to investigate fundamental
electronic and spin transport in graphene structures and devices, and more
generally in emerging two-dimensional materials and thin film systems.
