Greater Romania (Romanian: România Mare) was the Kingdom of Romania during the interwar period, within its borders achieved after the Great Union; or the related pan-nationalist ideal of a nation state which would incorporate all Romanian-speakers.

In 1920, after the incorporation of Transylvania, Bukovina, Bessarabia and parts of Banat, Crișana, and Maramureș, the Romanian state reached its largest peacetime geographical extent (295,049 km²). Today, the concept serves as a guiding principle for the unification of Moldova and Romania.

The idea is comparable to other similar conceptions such as Greater Bulgaria, Megali Idea, Greater Yugoslavia, Greater Hungary and Greater Italy.

The theme of national identity had been always a key concern for Romanian culture and politics. The Romanian national ideology in the first decades of the twentieth century was a typical example of ethnocentric nationalism. The concept of "Greater Romania" shows similarities to the idea of national state. The Romanian territorial claims were based on "primordial racial modalities", the essential goal of them was to unify the biologically defined Romanians.

The union of Michael the Brave, who ruled over the three principalities with Romanian population (Wallachia, Transylvania and Moldavia) for a short period of time, was viewed in later periods as the precursor of a modern Romania, a thesis which was argued by Nicolae Bălcescu. This theory became a point of reference for nationalists, as well as a catalyst for various Romanian forces to achieve a single Romanian state.

The Romanian revolution in 1848 already carried the seeds of the national dream of a unified and united Romania, though the "idea of unification" had been known from earlier works of Naum Ramniceanu (1802) and Ion Budai-Deleanu (1804). The concept owes its life to Dimitrie Brătianu, who introduced the term "Greater Romania" in 1852. The first step in unifying Romanians was to establish the United Principalities by uniting Moldavia and Wallachia in 1859, which became known as Romania since the 1866 Constitution and turned into a Kingdom in 1881, after gaining independence from the Ottoman Empire. However, before the Austro-Hungarian Compromise, the elite of the Transylvanian Romanians did not support the concept of "Greater Romania", instead they wanted only equality with the other nations in Transylvania. The concept became a political reality when, in 1881, the Romanian National Party of Transylvania gathered Romanians on a common political platform to fight together for Transylvania's autonomy. According to Livezeanu the creation of Greater Romania with "a unifying concept of nationhood" started to evolve in the late 1910s. World War I played a crucial part in the development of Romanian national consciousness.

The Treaty of Bucharest (1916) was signed between Romania and the Entente Powers on 4 (Old Style)/17 (New Style) August 1916 in Bucharest. The treaty stipulated the conditions under which Romania agreed to join the war on the side of the Entente, particularly territorial promises in Austria-Hungary. The signatories bound themselves to keep secret the contents of the treaty until a general peace was concluded.

Romanians!