The Aden Protectorate (Arabic: محمية عدن Maḥmiyyat ‘Adan) was a British protectorate in southern Arabia. The protectorate evolved in the hinterland of the port of Aden and in the Hadhramaut after the conquest of Aden by the Bombay Presidency of British India in January 1839, and which continued until the 1960s. In 1940, it was divided for administrative purposes into the Western Protectorate and the Eastern Protectorate. The territory now forms part of the Republic of Yemen.

The rulers of the Aden Protectorate, as generally with the other British protectorates and protected states, retained a large degree of autonomy: their flags still flew over their government buildings, government was still performed by them or in their names, and their states maintained a distinct 'international personality' in terms of international law, in contrast to states possessed directly by the British Empire, such as Colony of Aden, where the British monarch was the sovereign.

What became known as the Aden Protectorate began with informal arrangements of protection with nine states in the immediate hinterland of the port city of Aden, namely Abdali, Alawi, Amiri, Aqrabi, Aulaqi, Fadhli, Haushabi, Subeihi, and Yafa.

British expansion into the area was designed to secure the important port that was, at the time, governed from British India. From 1874, these protection arrangements existed with the tacit acceptance of the Ottoman Empire that maintained suzerainty of Yemen to the north, and the polities became known collectively as the "Nine Tribes" or the "Nine Cantons."

Beginning with a formal treaty of protection with the Mahra Sultanate of Qishn and Socotra in 1886, the British began a slow formalisation of protection arrangements that included more than 30 major treaties of protection with the last signed only in 1954. These treaties, together with a number of other minor agreements, created the Aden Protectorate that extended well east of Aden to Hadhramaut and included all of the territory that would become South Yemen except for the immediate environs and port of the colonial capital, Aden.

Aden with its harbour was the only area in full British sovereignty and, together with some offshore islands, was known as Aden Settlement (1839–1932), Aden Province (1932–1937), the Colony of Aden (1937–1963) and finally State of Aden (1963–1967).

In exchange for British protection, the rulers of the constituent territories of the Protectorate agreed not to make treaties with or cede territory to any other foreign power. In 1917, control of Aden Protectorate was transferred from the Government of India, which had inherited the British East India Company's interests in various princely states on the strategically important naval route from Europe to India, to the British Foreign Office. For administrative purposes, the protectorate was divided into the Eastern Aden Protectorate (with its own Political Officer, a British advisor, stationed at Mukalla in Qu'aiti from 1937 to c. 1967) and the Western Aden Protectorate (with its own Political Officer, stationed at Lahej from 1 April 1937 to 1967), for some separation of administration.

In 1928, the British established Aden Command, directed by the Royal Air Force, to preserve the security of the Protectorate. It was renamed British Forces Aden in 1936 and was known later as British Forces Arabian Peninsula and then Middle East Command (Aden).