This dissertation contributes to the field of macroeconomic theory, focusing on questions of monetary and fiscal policy using classic tools such as repeated games and mechanism design. The chapters explore how credibility, information asymmetries, and hidden actions shape policy implementation and its outcomes. The first chapter, "Debt, Inflation, and Government Reputation", introduces a dynamic game of incomplete information in which a government’s reputation for fiscal and monetary prudence evolves endogenously based on observed policy choices. Wage setters form expectations about inflation based on the perceived type of government (prudent or imprudent), which affects the correlation between debt and inflation. The model accounts for episodes in which high debt is associated with high inflation and others in which inflation remains stable despite rising debt. The theoretical predictions align with historical data from emerging markets such as Mexico, Colombia, Guatemala, and Thailand. The second chapter, "Public Good Provision and Optimal Taxation in a Hidden Savings World", studies a public good provision problem where the government cannot observe individual income or cash savings decisions; the government can only observe savings in the economy's formal system (a bank). This introduces an informational friction constraining taxation since cash represents an outside option for savings and has benefits from not being taxed. Using a mechanism design approach, the chapter characterizes the optimal tax schedule as a function of bank savings, showing that it must be non-decreasing and concave. This shape balances efficiency and redistribution by discouraging excessive savings concealment through cash while preserving incentives to save in the economy's formal system. These chapters offer insights into how governments can manage macroeconomic trade-offs in the presence of private information; as well as how credibility and enforcement limitations shape policy design.