Abstract
Percolation theory aims at the study of very simple models of disordered systems. I try to demonstrate how mechanical, electrical, superconducting, optical, etc. properties of thin semicontinuous metal films on dielectric substrates can be explained by percolation models and how various concepts and results of percolation theory ranging from the existence of a sharply defined percolation threshold to the most sophisticated issues such as that of the detailed structure of large percolation clusters can help in understanding the experimental observations.