This document provides an outline for a lecture on imperfections in solids. It will cover point defects like vacancies and self-interstitials, impurities and solid solutions, linear defects like dislocations, and interfacial defects such as grain boundaries and phase boundaries. The goal is for students to understand different types of crystalline defects and how they influence material properties. Imperfections are an important factor in determining behaviors like yield strength and how metals respond to alloying.