Several books have been published concerning the issue of immigrants during the past couple decades. Notable ones are M. Daniel Carroll R., The Bible and Borders: Hearing God’s Word on Immigration (Grand Rapids: Brazos, 2020); Mark W. Hamilton, Jesus, King of Strangers: What the Bible Really Says about Immigration (Grand Rapids: Eerdmans, 2019); James K. Hoffmeier, The Immigration Crisis: Immigrants, Aliens, and the Bible (Wheaton, IL: Crossway, 2009); Ched Myers and Matthew Colwell, Our God is Undocumented: Biblical Faith and Immigrant Justice (Maryknoll, NY: Orbis, 2012). While they touch the Old Testament laws about immigrants, they did not provide a thorough analysis of the four Pentateuchal law codes: Covenant Code (CC), Deuteronomic Code (DC), Priestly Code (PC), and Holiness Code (HC). Rather, they approach the Old Testament laws thematically and selectively when they are relevant. A careful analysis, however, shows each law code has its own characteristics concerning immigrants. In this paper, I will present a thorough analysis of the laws about immigrants in the four different Pentateuchal law code. The CC shows the earliest and less developed stage of the immigrant laws. The principle of the laws can be summarized as the prohibition of economic and legal oppression. The DC multiplies the immigrant laws and greatly develops the direction of the CC. On top of the principle of the prohibition of oppression of the CC, the DC develops charity laws, by which the society systematically and consistently supports economically less-privileged immigrants. While the DC focuses on the inclusion of immigrants in social, economic, and civic dimensions, the PC focuses on the issue of how to treat immigrants in religious or cultic matters. The basic principle of the PC is “the application of the same law” both for Israelites and immigrants. The HC updates the PC by incorporating “the prohibition of oppression” from the CC and “charity laws” from the DC. Emphasizing the priestly principle of the same application, the HC requires immigrants to stand as active participants of the Israelites faith traditions, not just staying as passive beneficiaries of protection and support of the community. At the same time, the HC develops the unique idea that even Israelites are like temporary immigrants in the land that belongs to God. The four Pentateuchal law codes show how the immigrant laws were developed and what were their primary motivations and theological foundations. The thorough analysis of each Pentateuchal law code and their synthesis teach us timeless lessons about the issues of immigrants, outsiders, or aliens.