  The electroweak symmetry may be broken by a composite Higgs which arises
naturally as a bound state of the top quark if the standard model gauge fields
and fermions propagate in extra dimenions. The top quark mass and the Higgs
mass can be predicted from the infrared fixed points of the renormalization
group equations. The top quark mass is in good agreement with the experimental
value, and the Higgs boson mass is predicted to be $\sim 200$ GeV. The bounds
on the compactification scale can be quite low if all standard model fields
propagate in the same extra dimensions due to the momentum conservation in
extra dimensions. The current lower limits are about 300 GeV for one extra
dimension and 400-800 GeV for two extra dimensions. The future collider
experiments may either discover the Kaluza-Klein (KK) states of the standard
model fields or raise their mass limits significantly. There may also be some
other light bound states which could be observed at upcoming collider
experiments.
