  This paper begins with a theoretical explanation of why spacetime is
discrete. The derivation shows that there exists an elementary length which is
essentially Planck's length. We then show how the existence of this length
affects time dilation in special relativity. We next consider the symmetry
group for discrete spacetime. This symmetry group gives a discrete version of
the usual Lorentz group. However, it is much simpler and is actually a discrete
version of the rotation group. From the form of the symmetry group we deduce a
possible explanation for the structure of elementary particle classes.
Energy-momentum space is introduced and mass operators are defined. Discrete
versions of the Klein-Gordon and Dirac equations are derived. The final section
concerns discrete quantum field theory. Interaction Hamiltonians and scattering
operators are considered. In particular, we study the scalar spin~0 and spin~1
bosons as well as the spin~$1/2$ fermion cases
