  We construct anomaly-free $U(1)_1\times U(1)_2\times...\times U(1)_m$ gauge
extensions of the Standard Model. To perform this construction we put together
anomaly-free $U(1)$ extensions of one and two families of fermions. The
availability of free parameters that enter linearly in the equations for the
fermion charges and the large number of different classes of extensions may
help other model builders interested in their use to solve problems of particle
physics.
