This document summarizes and compares classical and Keynesian economics. Classical economics is centered around self-regulating markets that operate at full employment, while Keynesian economics recognizes markets do not always self-adjust and the economy can operate below full employment. Key differences include classical economics believing free markets are always stable versus Keynesian thinking they are unstable. The document also outlines Keynesian principles like markets clearing slowly and government intervention being desirable to stabilize the business cycle through fiscal and monetary policies.