This Chapter is a selection from The Yellow Emperor’s Classic of Internal Medicine, specifically focusing on chapters discussing the nature of qi (vital energy) and its imbalances. It details the three types of qi—ancestral, nutritive, and defensive—and their roles in health and illness, particularly sleeplessness caused by evil qi. The text explores diagnostic methods and treatments, including a Pinellia Decoction recipe and acupuncture techniques. Furthermore, it describes correspondences between the human body and the natural world, explaining how various bodily parts relate to celestial and terrestrial elements, ultimately aiming to explain the principles of maintaining health through the harmonization of yin and yang.