  Decoupling a vectorial PDE consists in solving the system for each component,
thereby obtaining scalar PDEs that prescribe the evolution of each component
independently. We present a general approach to decoupling of Quantum Walks,
again defined as a procedure to obtain an evolution law for each scalar
component of the QW, in such a way that it does not depend on the other
components. In particular, the method is applied to show the relation between
the Dirac (or Weyl) Quantum Walk in three space dimensions with (or without)
mass term, and the Klein-Gordon (or wave) equation.
