This paper examines the impact of fair value accounting (FVA) on financial statement reliability and investor decisionmaking through a comparative analysis of International Financial Reporting Standards (IFRS) and local Generally Accepted Accounting Principles (GAAP). The study explores the conceptual frameworks, practical applications, and empirical evidence regarding fair value measurements across different accounting regimes. Findings indicate that while fair value accounting enhances relevance and improves decision usefulness for investors, concerns persist regarding reliability, particularly during market volatility and for assets with limited active markets. The comparative analysis reveals that IFRS generally permits more extensive application of fair value measurement compared to local GAAP systems, with significant implications for financial statement comparability and investment decision-making. The research contributes to the ongoing debate about the appropriate balance between relevance and reliability in financial reporting and offers insights for standard-setters, preparers, and users of financial statements in an increasingly globalized economic environment