Nosy Be (Malagasy pronunciation: [nusʲ be]; formerly Nossi-bé and Nosse Be, lit. 'big island') is a volcanic island off the northwest coast of Madagascar. Nosy Be is Madagascar's largest and busiest tourist destination. It has an area of 320.02 km² (123.56 sq mi), and its population was 109,465 according to the provisional results of the 2018 Census.

Nosy Be means "big island" in the Malagasy language. The island was called Assada by the French during the early 17th century. Nosy Be has been given several nicknames over the centuries, including "Nosy Manitra" (the scented island).

The first human inhabitants of Nosy Be were small bands from Antankarana and Zafinofotsy ethnic groups, before the Sakalava people migrated there and became the largest group on the island. These people were joined later by some Comorians, Indians and Antandroy. Nosy Be made its first major appearance in Madagascar's history when King Radama I announced that he intended to conquer the whole west of Madagascar. That plan was eventually achieved in 1837 when the Sakalava Kingdom of Boina came into the possession of Ranavalona I upon the defeat of Queen Tsiomeko's army.^{[citation needed]}

The French colonized the island from 1840, founding an outpost named Hell-Ville (from French Admiral de Hell). The 1848 abolition of slavery in the French colonies resulted in a revolt against the French by the Sakalava people, who were extensively involved in the slave trade. In the late 19th and early 20th centuries, the island was governed by the French as an internal protectorate within the colony of Madagascar. The outpost became an important trade harbor in the Mozambique channel.

During the nineteenth century, the French settlers developed cash crop agriculture (mainly sugar cane) and recruited indentured laborers from East Africa. Though it was difficult for the French to control the littoral, they founded a plantation colony in Nosy Be, mainly producing sugar and cash crops. The French used both military force and diplomacy to maintain their position in the island, appointing the former ruler of Nosy Be Binao as the gouverneur principal of the island.

During the Russo-Japanese War Nosy Be became a supply station for Russia's Second Pacific Squadron. The main fleet led by Admiral Zinovy Rozhestvensky reached Nosy Be on January 9, 1905, where it met a smaller detachment led by Admiral Dmitry von Fölkersam that had arrived already on December 28, 1904. The fleet stayed for two months for refurbishing and coaling, leaving on March 17 to meet its fate ten weeks later at the Battle of Tsushima.

In 2013, two French tourists and one local were lynched (beaten and burned by a mob) after rumors that they were responsible for the death of a local boy. A Madagascar court gave four men the maximum hard labour for life over the mob lynching.

Nosy Be is located about 8 kilometres (5.0 mi) from the coast of Madagascar in the Mozambique Channel; several smaller islands are located nearby, including Nosy Komba, Nosy Mitsio, Nosy Sakatia, and Nosy Tanikely. The island's main town is Andoany, commonly known as Hell-Ville.