A policy designed to provide protection against catastrophic losses. It generally is written over various primary personal and commercial liability policies. The umbrella policy serves three purposes: it provides excess limits when the limits of underlying liability policies are exhausted by the payment of claims; it drops down and picks up where the underlying policy leaves off when the aggregate limit of the underlying policy in question is exhausted by the payment of claims; and it provides protection against some claims not covered by the underlying policies, subject to the assumption, by the named insured, of a self-insured retention.