This document introduces mathematical induction. It defines the principle of mathematical induction as having two steps: (1) the basis step, which shows a statement P(1) is true, and (2) the inductive step, which assumes P(k) is true and shows P(k+1) is also true. It provides an example of climbing an infinite ladder to illustrate these steps. It also notes some important points about mathematical induction, such as that it is expressing a rule of inference and in proofs we show P(k) implies P(k+1) rather than assuming P(k) is true for all k.