  We argue that the shape of the system-size dependence of strangeness
production in nucleus-nucleus collisions can be understood in a picture that is
based on the formation of clusters of overlapping strings. A string percolation
model combined with a statistical description of the hadronization yields a
quantitative agreement with the data at $\sqrt{s_{NN}}=17.3$ GeV. The model is
also applied to RHIC energies.
