Being political scapegoats in the indefinite “war on terror” is the new normal for Muslims in America. With each federal election cycle or terrorist attack in a Western country comes a spike in islamophobia. Candidates peddle tropes of Muslims as terrorists in campaign materials and political speeches to solicit votes. Government officials call for bold measures—extreme vetting, categorical bans, and mass deportations—to regulate and exclude Muslim bodies from U.S. soil. The racial subtext is that Muslims in the United States are outsiders who do not belong to the political community. A case in point is the “Muslim ban” issued by the Trump administration in 2017. As the ban dominated public debate and litigation, another racialized counterterrorism policy lurked in the backdrop: a Muslim registry. This Article explores the political and legal plausibility of a de jure or de facto Muslim registry. Analyzing separately the case of nonimmigrants, immigrants, and U.S. citizens, the Article concludes that proponents of a nonimmigrant special registration program based on national origin will find support in the law. A registry of immigrants is also possible, though much will depend on whether courts will look to the islamophobic political environment arising from Trump and his advisor’s anti-Muslim statements to apply strict scrutiny; or whether courts will accept facially neutral national security justifications to apply the rational basis test that nearly guarantees the government’s victory. In contrast, a registry of U.S. citizen Muslims is unlikely to pass constitutional muster, as is a special registration program explicitly based on religion. Separate from the dignitary harms and privacy concerns arising from a Muslim registry are threats to the liberty of millions of people in America. A Muslim registry could very well be the precursor to mass internment should another major terrorist attack occur on U.S. soil. For that reason alone, proponents of civil rights and liberties should be prepared to oppose what is no longer unimaginable