In this chapter, I argue that the time is ripe for the interdisciplinary and quantitative study of comparative immigration law based on large-scale data. Written in a way that should be understandable also for scholars and students from other disciplines with little knowledge of political science and quantitative methods, and based on the state of the art in comparative political science, the chapter presents a toolbox of quantitative solutions to the methodological challenges that this enterprise faces. I begin by describing the constituent domains and the architecture of immigration law, and then address the key decisions involved in in devising adequate conceptual tools that clearly specify dimensions of interest for comparative analysis. After a short history of how the field of migration studies has evolved in terms of measurement, the next section explains the two basic approaches to social science measurement and then provides an overview of ten databases and datasets that can be used to quantify dimensions of immigration law. I then move on to tools for descriptive analysis and tools for causal analysis. While descriptive analysis maps variations in immigration law across space and time, causal analysis relies on comparisons that aim either to test causal explanations of variations in immigration law or to estimate causal effects of variations in immigration law on various social and individual-level outcomes. I present the key methodological tools for such analyses by unpacking some pertinent examples from the literature. I conclude by reflecting on the potentials for interdisciplinary cross-fertilizations between empirical legal scholars and quantitative political scientists in the field of comparative immigration law and its advancement through a common research agenda.