Abstract 
Over the past years and decades, numerous large-scale quantitative datasets to measure various attributes of immigration law have been generated and analyzed by researchers and teams with wide-ranging and diverse disciplinary backgrounds. Many of them have also employed quantitative methods for descriptive and/or causal analysis to address empirical puzzles emanating from various and often cross-cutting literatures. However, to further propel comparative immigration law forward and to make it a more important and methodologically sophisticated endeavor also for legal scholars, the research community in this field could use an overview of the current data and methods on offer. Against this background, based on the state of the art in quantitative comparative political science, the aim of this Working Paper is to equip students and scholars of other methodological and/or disciplinary backgrounds with the necessary knowledge to be able to understand, assess, and appreciate quantitative research in this area or to join this research enterprise themselves. To achieve this aim, the text is written in a way that is understandable also for readers with little knowledge of political science and quantitative methods. Meanwhile, in order to illustrate the potential of quantitative methods for comparative analyses of immigration law, the Working Paper also presents some key findings of pertinent examples in the existing literature. After describing the constituent domains and the architecture of immigration law, I address the key decisions involved in devising adequate concepts that clearly specify legal attributes of interest for comparative analysis. After a short history of how the measurement of migration-related laws has evolved, the following section explains the measurement methods and then provides an overview of ten existing databases and datasets that can be used to quantify various attributes of immigration law. I then move on to methods for descriptive analysis and methods 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 societal and individual-level outcomes. I conclude by reflecting on the potentials for interdisciplinary cross-fertilizations between legal scholars and quantitative social scientists in the field of comparative immigration law and its advancement through a common research agenda.