We’ve gone through enough material throughout the book that now we are ready to talk about design principles. Many of these principles have appeared already in the book with different names, and some may already be familiar to you. The goal of this chapter is to provide a short overview of each principle. We will go over SOLID, DRY, and a few others. For each principle, I will give a bit of background, explain what it is, and give some guidelines on when and when not to follow it.