  We construct simple unconstrained Lagrangian formulations for massless higher
spin fields in flat space of arbitrary dimension and on anti de Sitter
background. Starting from the triplet equations of Francia and Sagnotti, which
describe a chain of spin modes, we introduce an auxiliary field and find
appropriate gauge invariant constraints that single out the spin-s mode. The
resulting quartet of fields, thus describing an irreducible representation of
the Poincare group, is used to construct simple Lagrangian formulations, which
are local, free from higher derivative terms and use equal number of auxiliary
fields for an unconstrained description of any value of spin. Our method proves
to be most efficient for an unconstrained description of massless higher spin
fermions in anti de Sitter space. A relation of the minimal models with the
universal BRST approach is discussed.
