  This Thesis reviews some recent developments about higher-spin interactions
in flat and constant curvature backgrounds. Particular attention is given to
the ambient-space formulation of the problem, both at the cubic and at the
quartic order, with some emphasis on the structure of the solution to the
Noether procedure that can be expressed in terms of powers of the standard Yang
Mills amplitudes. We also highlight how some aspects of String Theory appear to
reflect key properties of Field Theory that go beyond its low energy limit.
