This chapter explains how a nation's GDP price index (GDP-PI) and real gross domestic product (RGDP) are determined in the goods and services (G&S) market by the forces of supply and demand. It shows how changes in these supply and demand forces cause predictable movements of the GDP-PI and RGDP. If a nation's GDP-PI is above the equilibrium level, surpluses arise, causing prices to fall, which means natural market forces should reduce or eliminate the excess. Prices are not the only economic variables that influence buyers' decisions. Consumer, business, and government demands are influenced by other, external factors, such as income levels, indebtedness levels, interest rates, exchange rates, expectations, new legislation, number of buyers, investment opportunities, and wealth. As was the case with demand, price is not the only economic variable that influences sellers' production decisions. Demand-pull inflation occurs when G&S demand rises. Cost-push inflation occurs when G&S supply falls. Reductions in G&S demand decrease a nation's GDP-PI and RGDP.