  We construct momentum space expansions for the wave functions that solve the
Klein-Gordon and Dirac equations for tachyons, recognizing that the mass shell
for such fields is very different from what we are used to for ordinary (slower
than light) particles. We find that we can postulate commutation or
anticommutation rules for the operators that lead to physically sensible
results: causality, for tachyon fields, means that there is no connection
between spacetime points separated by a timelike interval. Calculating the
conserved charge and 4-momentum for these fields allows us to interpret the
number operators for particles and antiparticles in a consistent manner; and we
see that helicity plays a critical role for the spinor field. Some questions
about Lorentz invariance are addressed and some remain unresolved; and we show
how to handle the group representation for tachyon spinors.
