This document outlines several theories of business cycles or trade cycles including climatic, psychological, innovation, monetary, over-investment, over-production, and Keynesian theories. It provides a brief overview of each theory, noting key aspects like how sunspots, optimism/pessimism of businessmen, money supply changes, innovations, interest rates, overproduction, and changes in aggregate demand and investment can influence economic expansions and contractions over time. The document also discusses some criticisms of each theory, such as unrealistic assumptions or other factors not considered.