Higher-Spin Interactions: three-point functions and beyond

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.