We report on ferroelectric field effect experiments in epitaxial oxide heterostructures consisting of the ferroelectric oxide Pb(Zr,Ti)O₃ and the metallic oxides GdBa₂Cu₃O₇ and SrRuO₃. To perform the experiments, we used conventional capacitor structures, as well as a scanning probe approach that allows one to control the local ferroelectric polarization without the use of permanent electrical contacts. In the case of the scanning probe approach, nanometer scale control of the ferroelectric domain structure can be achieved over large areas of up to 2500 μm². Nonvolatile, reversible electronic nanofeatures were written in Pb(Zr₀.₅₂Ti₀.₄₈)O₃ / SrRuO₃ heterostructures by switching the local polarization field of the ferroelectric layer, inducing a field effect in the thin (30 Å) SrRuO₃ layer that changes its sheet resistance by 7%. This doping technique permits one to write reversible, nonvolatile electronic structures without requiring traditional lithographic processing or permanent electrical contacts.