If you spend any time in the world of cross-border taxes, you start to notice a pattern: the hardest problems usually begin with a deceptively simple question—who gets to tax you? And the answer is rarely as simple as “the country where I live.” That’s because tax systems don’t rely on just one concept to decide who belongs in their net. They use citizenship, residency, and domicile. These terms sound similar, and people often use them interchangeably in casual conversation, but in tax law they mean very different things. For globally mobile individuals, understanding the difference matters. You can be a U.S. citizen, a tax resident of another country, and still have your long-term home base tied to a different jurisdiction altogether. Each label can trigger different tax consequences, different filing obligations, and different planning opportunities.