This Chapter is a dialogue from the Yellow Emperor's Classic of Internal Medicine, exploring the nature of malaria. Huangdi (the Yellow Emperor) questions Qi Bo, a renowned physician, about the disease's cyclical fevers, varied presentations (chills then heat, or vice versa), and underlying mechanisms involving the interplay of yin and yang energies. Qi Bo explains malaria's onset, progression, and treatment based on the movement of pathogenic qi along the body's meridians and its interaction with the defensive qi. The discussion covers different types of malaria and emphasizes the importance of timing in treatment, advising against intervention during the disease's peak.