The Monarch Butterfly Biosphere Reserve (Spanish: Reserva de Biosfera de la Mariposa Monarca) is a World Heritage Site containing most of the overwintering sites of the eastern population of the monarch butterfly. The reserve is located in the Trans-Mexican Volcanic Belt pine-oak forests ecoregion on the border of Michoacán and State of Mexico, 100 km (62 miles), northwest of Mexico City. Millions of butterflies arrive in the reserve annually. Butterflies only inhabit a fraction of the 56,000 hectares of the reserve from October–March. The biosphere's mission is to protect the butterfly species and its habitat.

Most of the overwintering monarchs from eastern North America are found here. Researchers discovered these areas in 1975. Presidential decrees in the 1980s and 2000 designated these still privately held areas as a federal reserve. The Reserve was declared a Biosphere Reserve in 1980 and a World Heritage Site in 2008. The reserve remains predominantly rural. Reserve administrators continue to be concerned with deleterious effects of illegal logging and tourism. Conservation efforts sometimes conflict with the interests of local farmers, community-based landowners, private land owners and indigenous people.