  Modern network-like systems are usually coupled in such a way that failures
in one network can affect the entire system. In infrastructures, biology,
sociology, and economy, systems are interconnected and events taking place in
one system can propagate to any other coupled system. Recent studies on such
coupled systems show that the coupling increases their vulnerability to random
failure. Properties for interdependent networks differ significantly from those
of single-network systems. In this article, these results are reviewed and the
main properties discussed.
