The authors measure math skills with a broader set of explanatory variables than have been used in previous studies. To identify what math skills are important for student success in introductory microeconomics, they examine (1) the student's score on the mathematics portion of the ACT Assessment Test, (2) whether the student has taken calculus, (3) whether the student has been required to take remedial mathematics, and (4) the student's score on a test of very basic mathematical concepts. All four measures have significant effects in explaining performance in an introductory microeconomics course. The authors find similar results, regardless of whether they use self-reported information from students or official administrative records from the university. The results suggest that improvements in student performance may depend on improved mastery of basic algebra. (Contains 13 endnotes.)