Cozumel (Mayan: Island of the Swallows) is an island in the Caribbean Sea off the eastern coast of Mexico's Yucatán Peninsula, opposite Playa del Carmen. It is one of the eight municipalities (municipios) of the state of Quintana Roo. Cozumel is a popular tourist destination renowned for its scuba diving. The main town on the island is San Miguel.

The island is about 48 km (30 miles) north-south and 16 km (10 miles) east-west, and is the largest island of Mexico. It is about 20 km (12 miles) from the mainland, and some 60 km (36 miles) south of Cancún. Nearly everybody in Cozumel lives in the town of San Miguel (pop. est. 90,000 in 2003), which is on the western shore. The rest of the island is low, flat, and densely vegetated.

The Maya are believed to have first settled Cozumel by the early part of the 1st millennium AD, and older Preclassic Olmec artifacts have been found on the island as well. The island was sacred to Ix Chel, the Maya Moon Goddess, and the temples here were a place of pilgrimage, especially by women desiring fertility. There are a number of ruins on the island, most from the Post-Classic period. The largest Maya ruins on the island were bulldozed to make way for an airplane runway during World War II. The ruins of San Gervasio are located approximately at the center of the island and are the largest remaining ruins.

The first Spanish visitor was Juan de Grijalva in 1518, and in the following year Hernán Cortés came with a fleet and destroyed many Maya temples. Some 40,000 Maya lived on the island then, but smallpox devastated them and by 1570 only 30 were left alive. In the ensuing years Cozumel was nearly deserted, used as a hideout by pirates from time to time. In 1848, the Caste War of Yucatán resulted in resettlement by refugees escaping the tumult. A plaque at the Museo Cozumel states Abraham Lincoln as U.S. president was close to purchasing the island of Cozumel as a place to send the freed slaves. The continued war in the Yucatan forced him to change his mind.

In 1959, Jacques Cousteau discovered the extent and beauty of Palancar, the coral reefs at the south of Cozumel and publicized it as one of the best places to go scuba diving in the world. Although the original airport was a World War II relic and was able to handle jet aircraft and international flights, a much larger airport was built in the late 1970s. This resulted in much greater tourism to Cozumel.

Scuba diving is still Cozumel's primary draw, mainly due to the healthy coral reef marine communities. These coral reefs are protected from the open ocean by the island's natural geography. In 1996, the government of Mexico also established the Cozumel Reefs National Marine Park, forbidding anyone from touching or removing any marine life within the park boundaries. Despite the importance of healthy reefs to Cozumel's tourist trade, a deepwater pier was built in the 1990s for cruise ships to dock, causing damage to the reefs, and it is now a regular stop on cruises in the Caribbean.

The island was struck directly by two Category 4 hurricanes during the 2005 Atlantic hurricane season, Hurricane Emily and Hurricane Wilma, which together devastated much of the infrastructure and tourism industry on the island. Several successful efforts have been made to reconstruct damaged areas.

Singer Kirsty MacColl died on this island, after a tragic accident on December 18, 2000 in which she was hit by a speedboat owned by Mexican supermarket millionaire Guillermo González Nova (owner of Comercial Mexicana). The original case resulted in minor penalties for a crew hand, but the Mexican authorities have recently agreed to re-open the case due largely to the efforts of the Justice for Kirsty campaign organized by Kirsty's mother. The campaign's supporters include U2's Bono.