This chapter establishes return and risk as the fundamental duality underpinning all investment decisions. It systematically examines key return metrics—Holding Period Return, ROE, and IRR—alongside essential risk measures including volatility, beta, maximum drawdown, and the Six-Sigma framework for tail events. Through long-term performance analysis across asset classes and styles, it demonstrates how risk and return interact in practice. The discussion further integrates these dimensions via risk-adjusted performance metrics like the Sharpe and Treynor ratios.