This is part of a series of lectures on Qin Bowei's 56 methods. The focus of this lecture is Deficiency and Deficiency conditions. This lecture discusses the source, causes, mechanism, locations, disease manifestations, and presenting symptoms providing a broad picture of Deficiency and its disorders. The associated treatment principles of Deficiency will also be discussed. This lecture also covers key diagnostic criteria for each principle, the associated flagship formula for each, how to modify it, as well as how it relates to classical Chinese medicine. The lecture will conclude with numerous case studies to demonstrate how the system can be used clinically.