  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.
