  Frustration in the presence of competing interactions is ubiquitous in the
physical sciences and is a source of degeneracy and disorder, giving rise to
new and interesting physical phenomena. Perhaps nowhere does it occur more
simply than in correlated spin systems, where it has been studied in the most
detail. In the past few years, a new perspective has opened in the study of
frustration through the creation of artificial frustrated magnetic systems.
These materials consist of arrays of lithographically fabricated single-domain
ferromagnetic nanostructures that behave like giant Ising spins. The
nanostructures' interactions can be controlled through appropriate choices of
their geometric properties and arrangement on a (frustrated) lattice. The
degrees of freedom of the material can not only be directly tuned, but also
individually observed. Experimental studies have unearthed intriguing
connections to the out-of-equilibrium physics of disordered systems and
non-thermal granular materials, while revealing strong analogies to (spin) ice
materials and their fractionalized magnetic monopole excitations, lending the
enterprise a distinctly interdisciplinary flavor. The experimental results have
also been closely coupled to theoretical and computational analyses,
facilitated by connections to classic models of frustrated magnetism, whose
hitherto unobserved aspects have here found an experimental realization. We
review the considerable experimental and theoretical progress in this field,
including connections to other frustrated phenomena, and we outline future
vistas for progress in this rapidly expanding field.
