  A percolation model is presented, with computer simulations for
illustrations, to show how the sales of a new product may penetrate the
consumer market. We review the traditional approach in the marketing
literature, which is based on differential or difference equations similar to
the logistic equation (Bass 1969). This mean field approach is contrasted with
the discrete percolation on a lattice, with simulations of "social percolation"
(Solomon et al 2000) in two to five dimensions giving power laws instead of
exponential growth, and strong fluctuations right at the percolation threshold.
