A firm grounding in single-input, single-output feedback theory leaves the reader well positioned to jump off into many other topics.Modern control theory as it is normally presented is such a blizzard of linear algebra that it can seem at first to have nothing at all to do with what appears in this book.The first section of this chapter offers a short bridge to that world. Next, this chapter treats an extremely common misunderstanding about oscillation, whose genesis is often an overinterpretation of phase margin. Finally, many students of "classical" control theory find themselves utterly at sea when it comes to applying their hard-earned knowledge to digitally controlled systems. The final section of this chapter aims to bridge that gap.