  Emergence of $\pi$-magnetism in open-shell nanographenes has been
theoretically predicted decades ago but their experimental characterization was
elusive due to the strong chemical reactivity that makes their synthesis and
stabilization difficult. In recent years, on-surface synthesis under vacuum
conditions has provided unprecedented opportunities for atomically precise
engineering of nanographenes, which in combination with scanning probe
techniques have led to a substantial progress in our capabilities to realize
localized electron spin states and to control electron spin interactions at the
atomic scale. Here we review the essential concepts and the remarkable advances
in the last few years, and outline the versatility of carbon-based
$\pi$-magnetic materials as an interesting platform for applications in
spintronics and quantum technologies.
