  We make a comprehensive study of indirect bounds on scalar leptoquarks that
couple chirally and diagonally to the first generation by examining available
data from low energy experiments as well as from high energy e+ e- and p pbar
accelerators. The strongest bounds turn out to arise from low energy data: For
leptoquarks that couple to right--handed quarks, the most stringent bound comes
from atomic parity violation. For leptoquarks that couple to left--handed
quarks, there are two mass regions: At low masses the bounds arise from atomic
parity violation or from universality in leptonic pi decays. At masses above a
few hundred GeV's, the dominant bounds come from the FCNC processes that are
unavoidable in these leptoquarks: The FCNC bound of the up sector, that arises
from D-Dbar mixing, combines with the FCNC bounds from the down sector, that
arise from rare K decays and K-Kbar mixing, to a bound on the flavour
CONSERVING coupling to the first generation.
  The bounds restrict leptoquarks that couple with electromagnetic strength to
lie above 600 GeV or 630 GeV for leptoquarks that couple to RH quarks, and
above 1040 GeV, 440 GeV, and 750 GeV for the SU(2)_W scalar, doublet and
triplet leptoquarks that couple to LH quarks. These bounds are considerably
stronger than the first results from the direct searches at HERA. Our bounds
also already exclude large regions in the parameter space that could be
examined by various methods proposed for indirect leptoquark searches.
