It has a land area of 80.763 square kilometres, the 12th-largest island in Mexico. Isla Partida's land area is 15.495 square kilometres. They are part of La Paz Municipality and are both a short boat trip from La Paz on the Baja California Peninsula.
The area is protected as part of the Área de Protección de Flora y Fauna - Islas del Golfo de California (APFF-IGC), and is an important eco-tourism destination. It was declared part of a Biosphere Reserve by UNESCO in 1995. Espíritu Santo is the only known habitat of the black jackrabbit. The islands are both uninhabited. Ensenada Grande beach, on Isla Partida, was voted the most beautiful beach in Mexico by The Travel Magazine and one of the top 12 beaches in the world. Sea kayaking is a popular activity around the island.
The surrounding reefs are home to parrotfish, angelfish, trumpetfish, Moorish idols, and rainbow wrasse, while many other species pass nearby including sharks, rays, turtles, dolphins, and even whales. Birds include brown pelicans, great blue herons, snowy egrets, turkey vultures, and hummingbirds. A large sea lion colony resides on Los Islotes, off the north tip of the islands; snorkeling with the females and young is a highlight of many tours.