The Canal du Midi (French pronunciation: [kanal dy midi]; Occitan: Canal del Miègjorn [ka'nal del mjɛdˈd͡ʒuɾ]) is a 240 km (150 mi) long canal in Southern France (French: le Midi). Originally named the Canal Royal en Languedoc (Royal Canal in Languedoc) and renamed by French revolutionaries to Canal du Midi in 1789, the canal is considered one of the greatest construction works of the 17th century.

The canal connects the Garonne to the Étang de Thau on the Mediterranean and, along with the 193 km (120 mi) long Canal de Garonne, forms the Canal des Deux Mers, joining the Atlantic to the Mediterranean.

Strictly speaking, "Canal du Midi" refers to the portion initially constructed from Toulouse to the Mediterranean – the Deux-Mers canal project aimed to link together several sections of navigable waterways to join the Mediterranean and the Atlantic: first the Canal du Midi, then the Garonne which was more or less navigable between Toulouse and Bordeaux, then the Garonne Lateral Canal built later, and finally the Gironde estuary after Bordeaux.

Jean-Baptiste Colbert authorized the start of work by royal edict in October 1666, with the aim of developing the wheat trade, under the supervision of Pierre-Paul Riquet, and construction lasted from 1666 to 1681, during the reign of Louis XIV. The Canal du Midi is one of the oldest canals of Europe still in operation (the prototype being the Briare Canal). The challenges in these works are closely related to the challenges of inland water transport today. The key challenge, raised by Pierre-Paul Riquet, was to convey water from the Montagne Noire (Black Mountains) to the Seuil de Naurouze, the highest point of the canal.

The Canal du Midi was inscribed as a UNESCO World Heritage Site in 1996, because of its outstanding engineering and artistic design, and it was designated as an International Historic Civil Engineering Landmark in 2016.

The Canal du Midi is located in the south of France, in the departments of Hérault, Aude, and Haute-Garonne. It is 240 kilometres (150 mi) long, starting in the west at Port de l'Embouchure, Toulouse and terminating in the east at Les Onglous, Marseillan, where the canal opens into the étang de Thau (between Agde and Sète).

The Canal du Midi is a summit-level canal, climbing from Toulouse on the Atlantic side over a distance of 52 kilometres (32 mi) to the Seuil de Naurouze or summit level, where the feeder canal enters. The total rise is 57.18 metres (187.6 ft), and the summit level is at an altitude of 189.43 metres (621.5 ft). This difference in level down to the sea is covered over the remaining distance of 188 kilometres (117 mi) from Naurouze to Les Onglous on the Étang de Thau.

The design canal depth is two metres (6.6 ft) with a minimum of 1.80 m (5.9 ft). The draft allowed is 1.50 m (4.9 ft) although regular users advise that even with 1.40 m (4.6 ft) boats will occasionally touch the bottom because of silt deposits in many places. The width on the surface is 20 m (66 ft) on average with variations between 16 m (52 ft) and 20 m (66 ft). Finally, the width of the canal bed is 10 m (33 ft).