This document summarizes the four laws of thermodynamics: 1) The Zeroth Law states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. 2) The First Law states that energy can be changed from one form to another but cannot be created or destroyed in an isolated system. 3) The Second Law states that the entropy of an isolated system always increases and approaches a maximum value at equilibrium. 4) The Third Law states that the entropy of a pure crystalline substance approaches zero as the temperature approaches absolute zero.