This document discusses the history and principles of passive solar design. It explains that passive solar design has been used since ancient times to heat buildings using sunlight without mechanical systems. Key aspects of passive solar design include apertures to admit sunlight, thermal mass to store heat, and distribution of stored heat. The document also covers passive cooling techniques like shade trees, overhangs, and natural ventilation. Daylighting strategies are discussed as well, such as skylights and clerestories, which provide natural light while reducing energy use. The overall goal of passive design is to efficiently use sunlight and natural ventilation to provide thermal comfort in an environmentally friendly way.