This volume presents mathematical formulas and theorems commonly used in economics. It includes both formulas like Roy`s identity that are peculiar to economics and formulas like Leibniz's rule that are common to many areas of applied mathematics. The volume is meant to be a reference work, to be used by students in conjunction with a textbook and by researchers in need of exact statements of mathematical results. The volume is the first grouping of this material for a specifically economist audience.