Yemen, officially the Republic of Yemen, is a country in West Asia. Located in southern Arabia, it borders Saudi Arabia to the north, Oman to the northeast, the south-eastern part of the Arabian Sea to the east, the Gulf of Aden to the south, and the Red Sea to the west, sharing maritime borders with Djibouti, Eritrea, and Somalia across the Horn of Africa. Covering roughly 455,503 square kilometres (175,871 square miles), with a coastline of approximately 2,000 kilometres (1,200 miles), Yemen is the second largest country on the Arabian Peninsula. Sanaa is its constitutional capital and largest city. Yemen's estimated population is 34.7 million, mostly Arab Muslims. It is a member of the Arab League, the United Nations, the Non-Aligned Movement and the Organisation of Islamic Cooperation.

Owing to its geographic location, Yemen has been at the crossroads of many civilisations for over 7,000 years. In 1200 BCE, the Sabaeans formed a thriving commercial kingdom that colonized parts of modern Ethiopia and Eritrea. In 275 CE, it was succeeded by the Himyarite Kingdom, which spanned much of Yemen's present-day territory and was heavily influenced by Judaism. Christianity arrived in the fourth century, followed by the rapid spread of Islam in the seventh century. From its conversion to Islam, Yemen became a center of Islamic learning, and Yemenite troops played a crucial role in early Islamic conquests. Much of Yemen's architecture survived until modern times. For centuries, it became a primary producer of coffee exported in the port of Mocha. Various dynasties emerged between the 9th and 16th centuries. During the 19th century, the country was divided between the Ottoman and British empires. After World War I, the Kingdom of Yemen was established, which in 1962 became the Yemen Arab Republic (North Yemen) following a coup. In 1967, the British Aden Protectorate became the independent People's Democratic Republic of Yemen (South Yemen), the first and only officially socialist state in the Arab world. In 1990, the two Yemeni states united to form the modern Republic of Yemen, with Ali Abdullah Saleh serving as the first president until his resignation in 2012 in the wake of the Arab Spring.

Since 2011, Yemen has been enduring a political crisis, marked by street protests against poverty, unemployment, corruption, and President Saleh's plan to amend Yemen's constitution and eliminate the presidential term limit. By 2015, the country became engulfed by an ongoing civil war with multiple entities vying for governance, including the Presidential Leadership Council of the internationally recognized government, and the Houthi movement's Supreme Political Council. This conflict, which has escalated to involve various foreign powers, has led to a severe humanitarian crisis.

Yemen is one of the least developed countries in the world, facing significant obstacles to sustainable development, and is one of the poorest countries in the Middle East and North Africa. In 2019, the United Nations reported that Yemen had the highest number of people in need of humanitarian aid, amounting to about 24 million individuals, or nearly 75% of its population. As of 2020, Yemen ranked highest on the Fragile States Index and second-worst on the Global Hunger Index, surpassed only by the Central African Republic. As of 2024, Yemen is regarded as the world's least peaceful country by the Global Peace Index. Additionally, it has the lowest Human Development Index out of all non-African countries. Yemen is one of the world's most vulnerable countries to climate change and among the least prepared to handle its effects.