This document summarizes key concepts from a chapter on product markets and national output. It discusses how gross domestic product is measured as the total value of final goods and services produced, consisting of consumption, investment, government spending, and net exports. Aggregate demand is determined by modeling consumption as a function of disposable income and investment as influenced by interest rates and profits. Product market equilibrium exists when aggregate demand equals aggregate supply at full employment output. Inflationary or recessionary gaps can occur when the economy is not at full employment level.