Multiemployer pension plans—created by collective bargaining agreements including more than one employer—cover more than 10 million workers and retirees, and are insured by the PBGC. In recent years, as a result of investment market declines, employers withdrawing from plans, and demographic challenges, many multiemployer plans have had large funding shortfalls and face an uncertain future. GAO examined (1) actions that multiemployer plans in the weakest financial condition have taken to improve their funding levels; (2) the extent to which plans have relied on PBGC assistance since 2009, and the financial condition of PBGC’s multiemployer plan insurance program; and (3) options available to address PBGC’s impending funding crisis and enhance the multiemployer insurance program’s future financial stability. GAO analyzed government and industry data and interviewed government officials, pension experts—including academics, actuaries, and attorneys, multiemployer plans’ trustees and administrators, employers and trade associations, unions, advocacy organizations, and other relevant stakeholders.