Oaxaca is one of the five Mexican states with the highest biological richness and one of the most diverse in ethnic composition. Knowledge and use of plant resources have been part of their culture and maintenance in territories with different ecological, geological, and climatic conditions. Oaxaca contains 43.9% of the Mexican flora, with about 10,229 vascular plant species, distributed in 26 vegetation types. Ethnobotanical research in Oaxaca has been conducted during decades, focused on aspects like the integral traditional management, traditional classification systems, floristic composition and management of different ecosystems, agroecosystems. This chapter synthesizes a panorama of the ethno-floristic inventory in some preserved areas of northeastern Oaxaca, in three Priority Terrestrial Regions (PTR) with high bio-cultural diversity. The study area comprised 84 municipalities with eight ethnic groups in the Tehuacán-Cuicatlán Valley, the Sierras del Norte de Oaxaca-Mixe and the Selva Zoque-La Sepultura. Ethnobotanical data were recorded by participative observation, ethnobotanic fieldtrips, and free interviews with the local guides, for almost 4 years. Specimens of useful plants were collected and photographed the vouchers deposited in UAM-IZ, MEXU, and OAX. Field information and photographs of each specimen were integrated into the database BIÓTICA (CONABIO 2012) and the images bank of CONABIO (2018). More than 2,340 specimens were collected, a total of 139 families, 441 genera, 804 species, 7 subspecies, and 18 varieties were identified. The genus Quercus was the richest one with 34 species, followed by Tillandsia L. (22 species), and Pinus L. (14). Most of the useful species were found in four vegetation types: montane cloud forests (MCF), oak forests (OF), pine forests (PF), and tropical semi-evergreen forest (TSF). We recorded 11 use categories, the most important being medicinal, edible, and ornamental plants. Variation in number of useful families and species among ethnic groups was detected. Those with the greatest number of useful species and botanical families are the Northern Zapotec, Mixe, and Mazatec people, whereas the ethnic groups with the lowest values of useful species and families are also distributed in few municipalities, like Mixtec and Nahua. Results of this research reinforce the statement that people of ethnic groups are local safeguards of biodiversity. Patterns of regeneration processes indicate high rates of resilience of ecosystems, which needs to be analyzed to understand the kinds of management that people practice to recovering vegetation, since apparently, ethnic groups of Northeastern Oaxaca assist empirically to ecosystems restoration. The total number of useful species recorded in the present study increase in almost 10% these records. For many localities these are the first records of useful plants. Traditional knowledge must persist by its own right to persist, because we must be clear and sensitive that there are many explanations of world and life.