How do totalization agreements interact with tax treaties, and are they the same thing?

They are different instruments that solve different problems. An income tax treaty allocates the right to tax income between two countries and reduces double income taxation through mechanisms like reduced withholding and residency tie-breakers. A totalization agreement, by contrast, coordinates the two countries' social security systems: it prevents you from paying social security taxes to both countries on the same wages and lets you combine work credits to qualify for benefits. Notably, the U.S. and India do not have a totalization agreement, so Indian nationals on temporary U.S. work visas may pay into both systems. Many other countries do have one with the U.S. So when someone says 'the treaty covers my social security,' clarify whether they mean the income tax treaty or a totalization agreement. Check the Social Security Administration's list of agreements at ssa.gov.