When most students first approachfeedback control, they are still coming to grips with its foundation inlinear system theory. This unsteadiness with thefoundationmakes understanding feedback dramatically moredifficult. Experienced professionals canhavesimilar problems, painfully compounded by the fog of imperfect memory of the linear system theorystudied years before. It is thusvery common for all types of students to sit down to study feedback, glimpse the breadth and depth of knowledge required as a prerequisite, and simply give up. The purpose of this chapter is to strengthen the reader in linear systemfundamentals. It will fill in the gaps for those who need gaps filled,deepen the understanding of thosefluent in the mechanics of solving problems but who were nevershown the overarching conceptual logic, and serve as a handy reference for those who are truly comfortable.