By higher-spin (HS) field one means generalizations of the electromagnetic potential or of the metric fluctuation that transform under arbitrary representations of the Lorentz group. Conceptual difficulties have long been identified in attempts to couple massless higher-spin modes in a Minkowski background. However, the key classic no-go theorems typically do not apply in the presence of infinite numbers of them. String Theory clearly leads the way to date, since its spectra involves a plethora of massive HS modes, however, a key question is whether String Theory itself is part of a more...