  We construct a worldline path integral for the effective action and
propagator of a Dirac field in 2+1 dimensions in an Abelian gauge field
background. Integrating over an auxiliary gauge group variable we derive a
worldline action depending only on $x(\tau)$, the spacetime paths. We show that
that action is a combination of a kinetic term plus a spin action. The first is
proportional to $\delta[\dot{x}^2(\tau)- 1]$. The second agrees exactly with
the spin action one should expect for a spin-1/2 field.
