  Depending on the point of view, the Casimir force arises from variation in
the energy of the quantum vacuum as boundary conditions are altered or as an
interaction between atoms in the materials that form these boundary conditions.
Standard analyses of such configurations are usually done in terms of ordinary,
equal-time (Minkowski) coordinates. However, physics is independent of the
coordinate choice, and an analysis based on light-front coordinates, where
$x^+\equiv t+z/c$ plays the role of time, is equally valid. After a brief
historical introduction, we illustrate and compare equal-time and light-front
calculations of the Casimir force.
