  This is an overview of the problem of the vacuum in light-cone field theory,
stressing its close connection to other puzzles regarding light-cone
quantization. I explain the sense in which the light-cone vacuum is
``trivial,'' and describe a way of setting up a quantum field theory on null
planes so that it is equivalent to the usual equal-time formulation. This
construction is quite helpful in resolving the puzzling aspects of the
light-cone formalism. It furthermore allows the extraction of effective
Hamiltonians that incorporate vacuum physics, but that act in a Hilbert space
in which the vacuum state is simple. The discussion is fairly informal, and
focuses mainly on the conceptual issues. [Talk presented at {\sc Orbis
Scientiae 1996}, Miami Beach, FL, January 25--28, 1996. To appear in the
proceedings.]
