The Sasang constitutional medicine or Sasang typology is a typological constitution medicine within traditional Korean medicine. It was systematized by Yi Je-ma in his book Dongyi Suse Bowon: Longevity and Life Preservation in Eastern Medicine in 1894. It is a branch of the yin-yang theory. It divides people into four body types based on their biopsychosocial traits and their nature of strong and weak organs. The classification was derived from the five body types of Traditional Chinese medicine described in an ancient Chinese medical book Lingshu Jing of Huangdi Neijing.