The Medicinal Plants Used by Native American Tribes in Southern California by Donna Largo, Daniel McCarthy, and Marcia Roper provides a resource guide for medical providers and traditional health care practitioners in an effort to better coordinate patient care with traditional practices. A secondary purpose is to make available information about traditional medicine to anyone interested in disease prevention through Native American knowledge and traditions. Plants have always played an important role in human history. Plants not only provide food but they can provide clothing, shelter, and medicine. Many plants contain hundreds of chemicals, and most have many active ingredients. Native American knowledge of plant uses is extensive. Current knowledge extends to more than one thousand plants that were used by all Native American Indians, and that is just a fraction of what was once known and used before European contact. Foods introduced by Europeans soon replaced traditional foods, but out of necessity, the practice of traditional plant medicine has survived. Through interviews with tribal elders, as well as information passed down to younger generations, we have been able to highlight thirty-one plants commonly used by Southern California Native American Tribes, which is the limited focus of this study. There are many more medicinal plants that we have documented, but we do not have the necessary data or chemical analysis to include them in this current project.