The fiscal impact of migration remains a globally debated issue, with various studies suggesting that the net fiscal impact of immigration is negligible. However, empirical results are highly sensitive to underlying assumptions and methodological choices, leading to divergent conclusions. This chapter critically examines the primary methodologies used to quantify the fiscal effects of migration, including generational accounting, and overlapping generations general equilibrium models. It explores how these methods affect the interpretation of fiscal contributions by migrants, particularly in relation to taxes, transfers, and public services. The chapter also discusses the potential biases and limitations inherent in these approaches, offering a comparative review of studies conducted in both high- and low-income countries. Further, it addresses key research gaps, including the impact of migration composition, emigration, and the relationship between migration and public debt. By highlighting the methodological diversity, the chapter aims to provide a more nuanced understanding of the fiscal consequences of migration, the factors influencing these results, and the policy implications.