This is a first course in mathematics. It is intended for home school students and parents interested in a book to support a classical discussion-based math curriculum. The main focus in this first volume is to develop the idea of number. We begin with counting by learning how the digits in a number count powers of ten. We then proceed through the arithmetic operations: addition, multiplication, division, and subtraction before turning to fractions. At each step we consider new insights into number that are revealed through the work of arithmetic or from thinking about representing quantity. An important secondary goal of the text is to prepare ideas that are helpful to more advanced studies in mathematics. More information is available at www.inletbooks.com.