The Sultanate of Ternate (Jawi: کسلطانن ترناتي‎), previously known as the Kingdom of Gapi, is one of the oldest Muslim kingdoms in Indonesia besides the sultanates of Tidore, Jailolo, and Bacan.

The Ternate kingdom was established by Momole Cico, the first leader of Ternate, with the title Baab Mashur Malamo, traditionally in 1257. It reached its Golden Age during the reign of Sultan Baabullah (1570–1583) and encompassed most of the eastern part of Indonesia and a part of southern Philippines. Ternate was a major producer of cloves and a regional power from the 15th to 17th centuries.

The dynasty founded by Cico continues to the present, as does the Sultanate itself, although it no longer holds any political power.

The sultanate was originally named the Kingdom of Gapi, but was later renamed for its capital, Ternate. Originally there were four villages in Ternate, led by clan leaders called Momole. The villages mainly traded spices with Arab, Malay, and Chinese traders. These lucrative trades attracted pirates and because of this, a kingdom emerged. According to one version, Momole Guna of Tobona suggested a forum in which a stronger organization of kingdom would be adopted. Momole Cico was elected to be the first Gapi king with regnal name Baab Mashur Malamo. According to another version, the ancestor of the Malukan kings was an Arab descendant of the Prophet called Jafar Sadik. Coming to Ternate, he encountered a nymph (bidadari) from heaven (kayangan) called Nurus Safa. Their four sons were the dynastic ancestors of Bacan, Jailolo, Tidore, and Ternate. The idea of a genealogical unity of the four realms of Maluku has had a large cultural significance that persists until the present. According to Ternatan legend, the youngest of the four sons, Baab Mashur Malamo, was born in heaven, and therefore enjoyed a special status. His descendants were sometimes known as Alam-ma-Kolano, "ruler of all [Maluku]".

Ternate along with neighbouring Tidore were the world's single major producer of cloves, due to which their rulers became among the wealthiest and most powerful sultans in the Indonesian region. Much of their wealth, however, was spent fighting each other. Until the Dutch completed the colonisation of Maluku in the 19th century, the Sultans of Ternate ruled realms that claimed at least nominal influence as far as Ambon, Sulawesi and Papua.

In part due to its trade-dependent culture, Ternate was one of the earliest places in the region to which Islam spread from Java in the late 15th century. However, Islamic influence in the area can be traced further back to the late 14th century. Initially, the faith was restricted to Ternate's small ruling family, and spread slowly to the rest of the population.

The royal family of Ternate converted to Islam during the reign of Marhum (1465–1486), making him the first King of Ternate that embraced Islam; his son and successor, Zainal Abidin (1486–1500) enacted Islamic Law and transformed the kingdom into an Islamic Sultanate; the title Kolano (king) was then replaced with Sultan.

The peak of Ternate's power came near the end of the 16th century, under Sultan Baabullah (1570–1583), when it had influence over most of the eastern part of Sulawesi, the Ambon and Seram area, Timor island, parts of southern Mindanao and Papuan Islands. It frequently engaged in fierce competition for control of its periphery with the nearby Sultanate of Tidore. According to historian Leonard Y. Andaya, Ternate's "dualistic" rivalry with Tidore is a dominant theme in the early history of the Maluku Islands.