An umbrella policy adds insurance limits to your existing coverage. A $1,000,000 umbrella policy adds $1,000,000 in limits to your Personal Liability (usually part of a Homeowners policy), and $1,000,000 to your automobile liability coverges. It will also increase other liability limits such as watercraft and employers liability (part of a Workers Compensation policy). Each insurance company issues a unique form. It is very difficult to compare these policies. Some policies will extend to cover exposures where you do not have "underlying" coverage. A deductible or "self insured retention" applies to insured losses that are not insured by any "underlying" policies. Unbrella policies requie that you purchase certain minimum limits of automobile and personal liability coverage.