  We study the implications of extra dimensions of size $R\sim 1/TeV$ on
electroweak and flavor physics due to the presence of Kaluza-Klein excitations
of the SM gauge-bosons. We consider several scenarios with the SM fermions
either living in the bulk or being localized at different points of an extra
dimension. Global fits to electroweak observables provide lower bounds on 1/R,
which are generically in the 2-5 TeV range. We find, however, certain models
where the fit to electroweak observables is better than in the SM, because of
an improvement in the prediction to the weak charge Q_W. We also consider the
case of softly-broken supersymmetric theories and we find new non-decoupling
effects that put new constraints on 1/R. If quarks of different families live
in different points of the extra dimension, we find that the Kaluza-Klein modes
of the SM gluons generate (at tree level) dangerous flavor and CP-violating
interactions. The lower bounds on 1/R can increase in this case up to 5000 TeV,
disfavoring these scenarios in the context of TeV-strings.
