The Bab-el-Mandeb (Arabic: باب المندب, lit. 'Gate of Grief/Tears') is a strait between Yemen on the Arabian Peninsula and Djibouti and Eritrea in the Horn of Africa, connecting the Red Sea to the Gulf of Aden and by extension the Indian Ocean.

In Bab-el-Mandeb, Bab means "gate" while Mandeb means "lamentation" or "grief". The strait derives its name from the dangers attending its navigation or, according to an Arab legend, from the numbers who were drowned by an earthquake that separated the Arabian Peninsula from the Horn of Africa.

Paleo-environmental and tectonic events in the Miocene epoch created the Danakil Isthmus, a land bridge forming a broad connection between Yemen and Ethiopia. During the last 100,000 years, eustatic sea level fluctuations have led to alternate opening and closing of the straits. According to the recent single origin hypothesis, the straits of Bab-el-Mandeb were probably witness to the earliest migrations of modern humans. It is presumed that the oceans were then much lower and the straits were much shallower or dry, which allowed a series of emigrations along the southern coast of Asia.

In Arab tradition it is reported that in ancient times Asia and Africa were joined together, until they were split at the Bab-el-Mandeb. Yaqut al-Hamawi associates the name Bab-el-Mandeb with the 6th century crossing of the Aksumites over the sea to Yemen. Two Sabaean inscriptions of the early 6th century mention silsilat al-Mandab in connection with the conflict between Dhu Nuwas and the Aksumites.

The British East India Company unilaterally seized the island of Perim in 1799 on behalf of its Indian empire. The government of Britain asserted its ownership in 1857 and erected a lighthouse there in 1861, using it to command the Red Sea and the trade routes through the Suez Canal. It was used as a coaling station to refuel steamships until 1935 when the reduced use of coal as fuel rendered the operation unprofitable.

The British presence continued until 1967 when the island became part of the People's Republic of South Yemen. Before the handover, the British government had put forward before the United Nations a proposal for the island to be internationalized as a way to ensure the continued security of passage and navigation in the Bab-el-Mandeb, but this was refused.

In 2008 a company owned by Tarek bin Laden unveiled plans to build a bridge named Bridge of the Horns across the strait, linking Yemen with Djibouti. Middle East Development LLC issued a notice to construct a bridge passing across the Red Sea that would be the longest suspended passing in the world. The project was assigned to engineering company COWI in collaboration with architect studio Dissing+Weitling, both from Denmark but the announced delay to Phase 1 in 2010 and the lack of any further updates since makes this a defunct project.

The Bab-el-Mandeb acts as a strategic link between the Indian Ocean and the Mediterranean Sea via the Red Sea and the Suez Canal. Most exports of petroleum and natural gas from the Persian Gulf that transit the Suez Canal or the SUMED Pipeline pass through both the Bab el-Mandeb and the Strait of Hormuz. While the narrow width of the strait requires vessels to travel through the territorial sea of adjacent states, under the purview of Article 37 of the United Nations Convention on the Law of the Sea, the legal concept of transit passage applies to Bab el-Mandeb, although Eritrea (unlike the rest of coastal countries) is not a party to the convention.