Abstract: Economists use math, but not always in ways a mathematician would find familiar. Many of our tools are specialized offshoots of older mathematical ideas which are simplified, repurposed, and deeply embedded in economic research. This talk offers a high-level tour of just a few widely used mathematical tools in economics, emphasizing both their mathematical roots and how economists have adapted them. I’ll cover three examples: the CES aggregator, foundational to models of international trade and monetary policy and closely related to what mathematicians call an L^p norm; recursive competitive equilibrium, a cornerstone of modern macroeconomic modeling built on Markov chains; and instrumental variables regression, an extension of traditional linear regression which economists use to think in a structured way about causality when experiments aren’t possible.