Government policy functions as a decisive force in financial markets, systematically reshaping corporate operating environments and driving asset repricing through monetary, fiscal, tax, trade, and regulatory channels. This chapter analyzes how policy instruments—including interest rate adjustments, fiscal stimulus, tax reforms, and regulatory shifts—directly influence corporate profitability and market valuations. It further highlights that policy impacts extend beyond immediate sectoral effects to alter competitive dynamics and capital allocation across markets. A critical distinction is emphasized between transient policy interventions and structural regime changes, underscoring the necessity for investors to integrate policy analysis into both macro allocation and security selection processes.