  We present a derivation of the recently discovered duality between the free
massless (2+1)-dimensional Dirac fermion and QED$_3$. Our derivation is based
on a regularized lattice model of the Dirac fermion and is similar to the more
familiar derivation of the boson-vortex duality. It also highlights the
important role played by the parity anomaly, which is somewhat less obvious in
other discussions of this duality in the literature.
