The Chiloé Archipelago (Spanish: Archipiélago de Chiloé, pronounced [tʃiloˈe], locally [ʃiloˈe]) is a group of islands lying off the coast of Chile, in the Los Lagos Region. It is separated from mainland Chile by the Chacao Channel in the north, the Sea of Chiloé in the east and the Gulf of Corcovado in the southeast. All islands except the Desertores Islands form Chiloé Province. The main island is Chiloé Island. Of roughly rectangular shape, the southwestern half of this island is a wilderness of contiguous forests, wetlands and, in some places, mountains. The landscape of the northeastern sectors of Chiloé Island and the islands to the east is dominated by rolling hills, with a mosaic of pastures, forests and cultivated fields.

The archipelago is known within Chile for its distinctive folklore, mythology, potatoes, cuisine and unique architecture. The culture of Chiloé is the result of mixing of Huilliche, Spanish and Chono influences in centuries of isolation without much contact with the rest of Chile or the Western World. Its cool temperate climate, abundance of sea resources and large and lush forests have also played a major role in shaping life in the islands.

In colonial times, Chiloé was an important bulwark in the defence against Dutch and British incursions to Chile and Patagonia. The archipelago was the last Spanish possession in Chile, successfully repelling patriot invasions until 1826. In the 19th century, the archipelago was a starting point for the Chilean colonisation of Patagonia. Not only were major expeditions assembled in Chiloé, but thousands of Chilotes migrated to the sparsely populated mainland to work in sheep-raising estancias, as railway navvies, or to become independent settlers. Belief in witchcraft has been common in the archipelago, reaching such influence that in 1880 Chilean authorities put on trial warlocks said to rule the archipelago through a secret society.

Once considered an isolated and backward part of Chile, today the archipelago retains its rural character despite increased connectivity and the growth of cities such as Ancud, Castro and Quellón. Since the 1990s, salmon aquaculture and tourism have been important sources of revenue in the archipelago, complementing traditional activities such as fishing and small-scale agriculture.

The Chiloé Province (Spanish: Provincia de Chiloé) includes all of the Chiloé Archipelago, except the Desertores Islands, plus the Guafo Island, for a total land area of approximately 9,181 square kilometres (3,545 square miles). The administrative center of the province is the city of Castro, while the episcopal see of the Roman Catholic bishopric is Ancud. The province of Chiloé is part of the Los Lagos Region (Región de los Lagos), which primarily consists of the Chilean lakes region on the mainland north of Chiloé; the administrative center of the region is Puerto Montt.

Chiloé Island is by far the largest island in the archipelago, at 8,394 square kilometres (3,241 square miles). It is roughly rectangular, with its long axis oriented from north to south. To the east of Chiloé Island lies the Sea of Chiloé, which contains most of the other islands in the archipelago. The Sea of Chiloé is a marginal sea separating Chiloé Island from Palena Province (also called Continental Chiloé). The main islands in the Sea of Chiloé are Quinchao, Lemuy, Tranqui, and Desertores Islands. To the northeast and southeast of the archipelago lie the Gulf of Ancud and the Gulf of Corcovado; the former is part of the Sea of Chiloé. Some 40 kilometres (25 miles) southwest of Chiloé Island lies Guafo Island, the southernmost island of the archipelago.

Chiloé Island is separated from the Chilean mainland by the 2-kilometre-wide (1.2-mile) Chacao Channel in the north. Most of the good harbors are located on the island's northern and eastern shores. The eastern shore is marked by a series of peninsulas and inlets, notably Estero de Castro where the capital, Castro, is located. The western part of Chiloé Island, as well as the whole of Guafo Island, is hilly and covered by forests. The hills are subdivided into two north–south ranges, Piuchén and Pirulil, separated by the lakes Cucao and Huillinco. They contain the highest points in the archipelago and do not exceed 800 metres (2,600 feet). Depressions in the western forest are occupied by numerous small lakes and bogs scattered across the landscape.

A bridge to the mainland is planned for the archipelago, despite opposition from some residents who fear pollution and habitat destruction. The Chacao Channel bridge would replace the ferry that connects the village of Chacao, Ancud Comuna, on Route 5 at the northern end of Chiloé Island, across the Chacao Channel with the village of Pargua, Calbuco Comuna, on the mainland.