Corporate governance refers to the system of rules, practices, and processes by which firms are directed and controlled. It shapes how power is exercised, how risks are managed, how decisions are made, and how stakeholder interests are balanced. Robust governance is widely hypothesised to improve firm performance by aligning managerial incentives with shareholder objectives, reducing agency costs, improving access to finance, and lowering cost of capital. Yet empirical evidence is nuanced: governance reforms sometimes yield clear performance gains, sometimes only affect valuation and cost of capital, and sometimes show heterogeneous effects across institutional contexts, ownership types, industries, and time horizons. This chapter synthesises theoretical foundations, surveys empirical findings, highlights measurement and identification challenges, proposes an empirical framework for research, and outlines policy and managerial implications. It concludes with directions for future work focused on causality, mechanisms, and contextual heterogeneity.