We describe how to use ZFITTER, a program based on a semi-analytical approach to fermion pair production in e+e- annihilation and Bhabha scattering. A flexible treatment of complete ${ \cal O}(\alpha)$ QED corrections, also including higher orders, allows for three calculational { \bf chains} with different realistic sets of restrictions in the photon phase space. { \tt ZFITTER} consists of several { \bf branches} with varying assumptions on the underlying hard scattering process. One includes complete ${ \cal O}(\alpha)$ weak loop corrections with a resummation of leading higher-order terms. Alternatively, an ansatz inspired from S-matrix theory, or several model-independent effective Born cross sections may be convoluted. The program calculates cross sections, forward-backward asymmetries, and for $\tau$~pair production also the final-state polarization. Various { \bf interfaces} allow fits to be performed with different sets of free parameters.
Categories: hep-ph