Limits on new physics from $e^+ e^- \to f\overline{f}$ with the ALEPH detector at LEP2

Preliminary ALEPH cross section and forward-backward asymmetry measurements are summarized for the process e+e- -> f fbar at centre of mass energies of up to 189 GeV. The results are used to place constraints on physics beyond the Standard Model, such as four-fermion contact interactions, leptoquarks, R-parity violating squarks and sneutrinos, and Z' bosons.