Greater Somalia, also known as Greater Somaliland (Somali: Soomaaliweyn; Arabic: الصومال الكبرى, romanized: al-Sūmāl al-Kubrā), is the geographic location comprising the regions in the Horn of Africa in which ethnic Somalis live and have historically inhabited.

During the Scramble for Africa at the end of the 19th century, Somali-inhabited territories were partitioned between imperial powers. The unification of these territories became a focal objective of an independent Somalia. Referred to as "Greater Somalia," these regions, at the outset of Somali independence, encompassed State of Somaliland (former British Somaliland) and Trust Territory of Somaliland (former Italian Somaliland), which had successfully merged into a single nation in 1960. French Somaliland, the Northern Frontier District (NFD) in Kenya, and the Ogaden region in Ethiopia were placed under the control of neighboring states, despite the pre-independence unification efforts of Somali nationalists.

The post-independence governments of the Somali Republic (1960–1969) and the Somali Democratic Republic (1969–1991) expended significant effort towards the unification of the NFD and French Somaliland with Somalia; however, their primary focus was the Ogaden region, which had been occupied by Ethiopia since Menelik's invasions in the 1890s. From 1960 onwards, Somalis in Ethiopia and Kenya seeking self-determination have waged several insurgencies with the support of neighbouring Somalia, such as the Shifta War, escalating into several major interstate conflicts including the 1964 Ethio-Somali War and 1977 Ogaden War in Ethiopia.

However, following the breakout of the Somali Civil War and the splintering of Somalia into various autonomous polities, the concept of Greater Somalia has seen a decline in support, with some Somali diaspora communities advocating for autonomy or secession rather than a fully-fledged union.

Since the early 20th century, the vision of Greater Somalia has taken shape, aiming to unite all Somali-inhabited regions in the Horn of Africa into a single nation. This concept, known as Pan-Somalism, seeks to consolidate these territories into one cohesive Somali state. The pursuit of this ideal has fueled conflicts, notably Somalia’s role in the Ogaden War with Ethiopia over the Somali Region and its support for Somali insurgents against Kenya. In 1946, the Somali Youth League proposed Harar as the future capital of Greater Somalia, dispatching delegates to the United Nations office in Mogadishu to advocate for this vision.

The colonisation of Somali territories during the Scramble for Africa in the late 19th and early 20th centuries involved multiple European powers and the Ethiopian Empire, driven by strategic and economic interests. The United Kingdom, France, and the Kingdom of Italy were the primary colonial powers vying for control of Somali-inhabited regions, motivated mainly by the need for trade routes and geopolitical dominance. Emperor Menelik's expansion into Somali inhabited territory coincided with the European colonial advances in the Horn of Africa, during which the Ethiopian Empire imported a significant amount of arms from European powers. The large scale importation of European arms completely upset the balance of power between the Somalis and the Ethiopian Empire, as the colonial powers blocked Somalis from receiving firearms.

Britain established a protectorate in northern Somalia (modern-day Somaliland) by signing treaties with the local Isaaq clans in the 1880s, guaranteeing nominal independence but controlling trade and order at ports like Berbera. Many of these clans had signed the protection treaties with the British in response to Ethiopian Emperor Menelik's Invasions. The agreements dictated the protection of Somali rights and the maintenance of independence.

France developed Djibouti as a coaling station, formalising French Somaliland in 1884, which remained a colony until 1977 when it later became the Republic of Djibouti. Italy also acquired southern Somali territories, establishing Italian Somaliland by 1889.