The present chapter is devoted, first, to discuss in detail the structure and results of Wallis's major and most influential mathematical work, the Arithmetica Infinitorum ([51]). Next we will revise Wallis's views on indivisibles as articulated in his answer to Hobbes's criticism in the early 1670s. Finally, we will turn to his discussion of the proper way to understand the angle of contingence in the first half of the 1680s. As we shall see, there are marked differences in the status that indivisibles seem to enjoy in Wallis's thought along his mathematical career. These differences correlate with the changing context of 17th-century mathematics from the 1650s through the 1680s, but also respond to the different uses Wallis gave to indivisibles in different kinds of texts—purely mathematical, openly polemical, or devoted to philosophical discussion of foundational matters.