The land reform in interwar Yugoslavia was a process of redistribution of agricultural land in the Kingdom of Serbs, Croats and Slovenes (renamed Yugoslavia in 1929) carried out in the interwar period. The reform's proclaimed social ideal was that the land belongs to those who work it. An unrealistically idyllic image of Serbian villages in the region of Šumadija was touted as the model of national awareness and peasant liberty sought by the reform, which was aimed at dismantling remnants of serfdom and sharecropping in parts of the country, as well as at breaking up large agricultural estates.

Approximately two thirds of the land expropriated and distributed by the land reform was located on the territory of the present-day Bosnia and Herzegovina. All parts of the country were subject to the reform, except the territory of the former Principality of Serbia (corresponding to the northern part of pre-World War I Serbia). A total of 1,924,307 hectares (4,755,070 acres) of land was redistributed, and more than 600,000 families received plots of land, through implementation of the reform.

Internal colonisation was a significant element of the land reform. It consisted of awarding the expropriated land to colonists—Royal Serbian Army volunteers, landless peasants resettled from poorer parts of the country, Yugoslav citizens moving to the country from neighbouring countries, and even those who usurped agricultural land on their own initiative and without any formal authorisation. Preference was given to the volunteers and supporters of the Yugoslav authorities. The colonisation process was used by the Yugoslav authorities as a means of ethnic engineering, seeking to increase the proportion of South Slavic peoples (predominantly Serbs), especially in border regions such as Banat, Bačka and Baranja and the present-day territories of Kosovo and North Macedonia. Most of the colonists arrived from Serbia.

Implementation of the land reform relied largely on the Interim Decree on the Preparation of the Agrarian Reform promulgated in 1919, supplemented by a number of ministerial-level orders and regulations. An act regulating the reform was enacted in 1931. The reform and colonisation were conducted against the backdrop of ethnic violence against the Moslem population in Bosnia and Herzegovina; in Kosovo, guerilla warfare waged by the Internal Macedonian Revolutionary Organisation; and civil unrest elsewhere. In Dalmatia, the reform was delayed by the question of the unresolved border with the Kingdom of Italy, relations with the Italian minority, and enjoyment of property rights of Italian citizens in Yugoslavia. The reform and colonisation contributed to ethnicisation of politics in Yugoslavia.

The Kingdom of Serbs, Croats and Slovenes (subsequently renamed Yugoslavia) was established by a proclamation of Prince Regent Alexander of Serbia on 1 December 1918. The proclamation was made in response to a petition presented by a delegation of the National Council of Slovenes, Croats and Serbs; it created a unified South Slavic state composed of the short-lived State of Slovenes, Croats and Serbs and the Kingdom of Serbia. Serbia had annexed the territories of Banat, Bačka and Baranja (also referred to as Vojvodina) and the Kingdom of Montenegro in the immediate aftermath of World War I. The additions of Vojvodina and Montenegro followed the annexation of Sandžak and areas of present-day Kosovo and North Macedonia in the immediate aftermath of the 1912–1913 Balkan Wars. Those territories were organised as the province of South Serbia. The State of Slovenes, Croats and Serbs comprised areas of the former Austria-Hungary that were inhabited by South Slavs, specifically in the Slovene Lands, Croatia-Slavonia, Dalmatia, and Austro-Hungarian Condominium of Bosnia and Herzegovina.

The provinces of Yugoslavia enjoyed different levels of development and had different legislation in place. The Slovene Lands were organised similarly to the Cisleithanian (Austrian) part of the former Austria-Hungary, while Croatia-Slavonia had been previously linked more closely to the Kingdom of Hungary. Ownership models resembling feudalism were widespread in Bosnia and Herzegovina, South Serbia, and Dalmatia. Bosnia and Herzegovina, as well as South Serbia, drew on their Ottoman heritage, but there were differences in various parts of those territories as well. Parts of Dalmatia were occupied by the Italian Army, which was attempting to enforce the Italian territorial award made under the Treaty of London.

No ethnic group constituted the majority of the population of Yugoslavia. The Serbs were the most numerous, accounting for almost 39% of inhabitants of the country. Croats and Slovenes constituted nearly 24% and 9% of the population, respectively. The first Yugoslav government considered the three groups as three "tribes" of a single nation, in line with the ideology of Yugoslavism. In practice, Serbs dominated the government, which became highly centralised. Parts of the country saw civil unrest, looting by armed groups, and revolutionary movements. In Croatia-Slavonia and in Vojvodina, those were largely associated with the Green Cadres or inspired by the Hungarian Soviet Republic. In South Serbia, Albanians in the Kachak Movement resisted the new state, and there was a pro-Bulgarian, anti-Yugoslav struggle championed by the Internal Macedonian Revolutionary Organisation (IMRO). In Montenegro, civil war, known as the Christmas Uprising, broke out.

The land reform was one of the first steps taken by the authorities of the newly established Yugoslavia. On 24 December 1918, within the four weeks following the proclamation of Yugoslavia, Regent Alexander issued a declaration asking peasants to calmly wait for the state to settle the agrarian question and give them land that will be "only God's and theirs". Two weeks later, on 6 January 1919, Alexander published a manifesto declaring his wish for an urgent and just agrarian reform. Alexander's manifesto was in line with the declaration of the Serbian government made in February 1917, after the Serbian defeat in the World War I Serbian campaign, promising land to those voluntarily joining the Royal Serbian Army. The manifesto was also in line with the November 1918 declaration of the National Council of Slovenes, Croats and Serbs. Faced with the civil unrest associated with the Green Cadres, the National Council promised land to every peasant. New Yugoslav authorities feared unrest caused by former soldiers returning to impoverished homes after the war, especially former prisoners of war captured by the Russian Empire who had seen the Bolshevik Revolution first hand. The main objective of the land reform appeared to be forging closer ties between the peasantry and the monarchy, to reduce the likelihood of a revolution.