Capital structure is an important element of any business organization. Every concern tries to have optimum capital structure in the view of increasing profitability, reducing overall cost of capital and thereby increasing value. Some authors have propounded theories of capital structure. Subsequently they were supported and criticized by many studies made over a period of time. The present paper has attempted to give important theories of capital structure and presented the studies which had supportive evidences and which have results against the recent theories of capital structure. The paper has presented net income approach, net operating income approach to capital structure, Modigliani and Miller theory of capital structure, Trade-off theory, pecking order theory and Market timing theory of capital structure with its chronological relevance.