  The wave function in relativity is defined, in four-dimensional space, on a
space-like three-dimensional plane. The plane, most close to the time-like
region, is the light-front plane $ct+z=0$. Corresponding dynamical approach -
the light-front dynamics - has considerable advantages. We describe, in a
field-theoretical framework, the construction of light-front dynamics and
illustrate it by some examples.
