Has someone ever told you that "some infinities are bigger than others?" Does that not make much sense? In this class, we'll dip our toes into set theory, the language behind most modern math. Specifically, we will explore cardinality, the art of telling when one group of things is bigger than another, using the power of an underappreciated tool you already know: matching. Along the way, you will encounter a hypothetical hotel and at least two kinds of infinity. By the end, you will be equipped with ideas that broke math less than 150 years ago. (Disclaimer: the first person to study these ideas lost his mind. Enroll at your own risk.)