  The extremely large electromagnetic fields generated in heavy-ion collisions
provide access to novel observables that are expected to constrain various key
transport properties of the quark-gluon plasma and could help solve one of the
outstanding puzzles in QCD: the strong CP problem. In this review we present a
brief overview of the theoretical and experimental characterization of these
electromagnetic fields. After reviewing the current state, emphasising one of
the observables -- the charge-dependent flow -- we discuss the various
discrepancies between the measurements and theoretical predictions. Finally, to
help resolve the discrepancies, we suggest new measurements and theoretical
ideas.
