Coordination of Benefits (COB) establishes the order of payment when two or more medical plans (primary and secondary) cover an individual and makes sure that no insured person receives more than 100 percent of the allowable expenses for an insured service. The primary plan pays benefits as it would without the presence of a secondary plan. A secondary plan reduces its benefits so that the total benefits provided by both it and the primary plan are not more than the total allowable expenses.