  We examine the phenomenological implications of a 200 GeV leptoquark in light
of the recent excess of events at HERA. Given the relative predictions of
events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks
may be excluded, including those contained in E_6 GUT models. It is shown that
future studies with polarized beams at HERA could reveal the chirality of the
leptoquark fermionic coupling and that given sufficient luminosity in each
e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The
implications of 200-220 GeV leptoquarks at the Tevatron are examined. While
present Tevatron data most likely excludes vector leptoquarks and leptogluons
in this mass region, it does allow for scalar leptoquarks. We find that while
leptoquarks have little influence on Drell-Yan production, further studies at
the Main Injector are possible in the single production channel. We investigate
precision electroweak measurements as well as the process e^+e^-\to q\bar q at
LEP II and find they provide no further restrictions on these leptoquark
models. We then ascertain that cross section and polarization asymmetry
measurements at the NLC provide the only direct mechanism to determine the
leptoquark's electroweak quantum numbers. The single production of leptoquarks
in \gamma e collisions by both the backscattered laser and Weisacker-Williams
techniques at the NLC is also discussed. Finally, we demonstrate that we can
obtain successful coupling constant unification in models with leptoquarks,
both with or without supersymmetry. The supersymmetric case requires the GUT
group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.
