  The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a
pair-conversion telescope designed to detect photons with energies from 20 MeV
to > 300 GeV. The pre-launch response functions of the LAT were determined
through extensive Monte Carlo simulations and beam tests. The point-spread
function (PSF) characterizing the angular distribution of reconstructed photons
as a function of energy and geometry in the detector is determined here from
two years of on-orbit data by examining the distributions of \gamma rays from
pulsars and active galactic nuclei (AGN). Above 3 GeV, the PSF is found to be
broader than the pre-launch PSF. We checked for dependence of the PSF on the
class of \gamma-ray source and observation epoch and found none. We also
investigated several possible spatial models for pair-halo emission around BL
Lac AGN. We found no evidence for a component with spatial extension larger
than the PSF and set upper limits on the amplitude of halo emission in stacked
images of low and high redshift BL Lac AGN and the TeV blazars 1ES0229+200 and
1ES0347-121.
