1. Market equilibrium occurs when the quantity demanded equals the quantity supplied at the equilibrium price. A shortage or surplus results when these quantities are not equal. 2. When demand or supply changes, the equilibrium price adjusts accordingly. An increase in demand raises price, while an increase in supply lowers price. 3. Government policies like price ceilings and price floors can disrupt market equilibrium by creating shortages or surpluses. Price ceilings set below the equilibrium price result in shortages, while price floors set above equilibrium price create surpluses.