This chapter is focused on convex functions. The information in the first six sections is basic and is easy to master. Section 2 introduces the subject. Section 3 shows that each convex function lies on or below its “chords.” Section 19.4 shows that each convex function satisfies “Jensen’s inequality.” Section 19.5 shows that a function is convex if and only if its “epigraph” is a convex set. Section 6 provides a variety of ways in which to determine whether or not a give function is convex.