Some of mathematics teaching is routine, like an exercise from a textbook for which you have received instruction and already know what to do. On other occasions, however, teaching mathematics is challenging, involving problems of teaching for which the solutions may not be readily apparent. These situations require the application of mathematical knowledge in concert with other types of knowledge for teaching. In this article, we explore the idea that teachers of mathematics act as applied mathematicians in applying mathematical knowledge to the resolution of teaching problems. This task involves the complex interplay of mathematical and teaching knowledge and processes of problem solving with success judged according to how well students learn. The article discusses these ideas through an examination of seven scenarios. (Contains 3 figures and 1 table.)