The Kumeyaay Indians (also 'Iipay--Tiipay, Ipai--Tipai, or Diegueño in the United States, or Kumiai in Mexico) have inhabited the landscapes of northern Baja California, Mexico, and southern California since long before European contact, originally making a living as mobile hunting, gathering, and fishing peoples in the region's varied environments. The division of Kumeyaay territory in 1848 by two distinct nation states imposed on the region an international boundary as well as separate political and economic structures, cultures, and languages. Historical processes have reduced Kumeyaay territory and population, and transformed indigenous lifeways, yet a few elder Kumeyaay still speak their native language and maintain cultural knowledge of the environment. In this thesis, I explore the questions of how contemporary ethnobotanical knowledge of Baja California's Kumeyaay Indians can make new contributions to scientific research of diachronic human-plant interactions in the study area, and how this knowledge can inform Kumeyaay cultural and linguistic revitalization through its incorporation in interpretive exhibits. I synthesize information from interviews conducted with 16 Kumeyaay plant specialists, documenting Kumeyaay knowledge of traditional uses for 47 native plants as food, medicine, tools, construction materials, and ritual resources, covering indigenous nomenclature, plant scheduling, harvesting, processing, and consumption, as well as cultural meanings associated with plants. I review archaeological, historical, ethnographic, linguistic, and botanical literature to situate the Kumeyaay ethnobotanical data in a regional and diachronic context. I discuss how this study contributes new information on the Kumeyaay and their interactions with the vegetative environment, and provide examples of how I have applied this information to support efforts toward Kumeyaay cultural and linguistic revitalization.