Electrons in low energy condensed matter physics are typically treated using
the non-relativistic Schrodinger or Pauli equations, with relativistic effects
included, if at all, via corrections of order v/c. We show that using the full Dirac
equation with 4-component spinors leads to a number of important qualitative
effects and, perhaps surprisingly, some striking simplifications over the
conventional lower energy treatments, already for nuclei with Z >2.