By definition and longstanding principle, excess liability insurance comes into play not until all other valid insurance has been exhausted in paying a loss. However, if the primary limits have not been exhausted due to payment of claims, but rather, are not available to apply to existing claims due to the insolvency of the primary carrier, is the excess insurer required to fill the void and drop down to pay the sums that the insured has become legally obligated to pay? This article explores the current legal thinking on the subject.