  In front-form dynamics the current operator can be constructed from auxiliary
operators, defined in a Breit frame where initial and final three-momenta of
the system are directed along the $z$ axis. Poincar\'e covariance constraints
reduce for auxiliary operators to the ones imposed only by kinematical
rotations around the $z$ axis.
  Elastic and transition form factors can be extracted without any ambiguity
and in the elastic case the continuity equation is automatically satisfied,
once Poincar\'e, ${\cal P}$ and ${\cal T}$ covariance, together with
hermiticity, are imposed. Applications to deep inelastic structure functions in
an exactly solvable model and to the calculation of the deuteron
electromagnetic form factors are presented.
