  A complete and explicit classification of generalized, or local, symmetries
of massless free fields of spin $s \geq 1/2$ is carried out. Up to equivalence,
these are found to consists of the conformal symmetries and their duals, new
chiral symmetries of order $2s$, and their higher-order extensions obtained by
Lie differentiation with respect to conformal Killing vectors. In particular,
the results yield a complete classification of generalized symmetries of the
Dirac-Weyl neutrino equation, Maxwell's equations, and the linearized gravity
equations.
