Land reform (also known as agrarian reform) involves the changing of laws, regulations, or customs regarding land ownership, land use, and land transfers. The reforms may be initiated by governments, by interested groups, or by revolution.

Land reform is often considered a contentious process, as land is a key driver of a wide range of social, political and economic outcomes. The structure and distribution of land rights has been linked to state formation, economic growth, inequality, political violence, and identity politics, making land reform highly consequential for the long-term structures of society.

Land reform may consist of a government-initiated or government-backed property redistribution, generally of agricultural land. Land reform can, therefore, refer to transfer of ownership from the more powerful to the less powerful, such as from a relatively small number of wealthy or noble owners with extensive land holdings (e.g., plantations, large ranches, or agribusiness plots) to individual ownership by those who work the land. Such transfers of ownership may be with or without compensation; compensation may vary from token amounts to the full value of the land.

Land reform may also entail the transfer of land from individual ownership—even peasant ownership in smallholdings—to government-owned collective farms; it has also, in other times and places, referred to the exact opposite: division of government-owned collective farms into smallholdings. The common characteristic of all land reforms is modification or replacement of existing institutional arrangements governing possession and use of land. Thus, while land reform may be radical in nature, such as through large-scale transfers of land from one group to another, it can also be less dramatic, such as regulatory reforms aimed at improving land administration.

Land ownership and tenure can be perceived as controversial in part because ideas defining what it means to access or control land, such as through "land ownership" or "land tenure", can vary considerably across regions and even within countries. Land reforms, which change what it means to control land, therefore create tensions and conflicts between those who lose and those who gain from these redefinitions (see next section).

Western conceptions of land have evolved over the past several centuries to place greater emphasis on individual land ownership, formalized through documents such as land titles. Control over land may also be perceived less in terms of individual ownership and more in terms of land use, or through what is known as land tenure. Historically, in many parts of Africa for example, land was not owned by an individual, but rather used by an extended family or a village community. Different people in a family or community had different rights to access this land for different purposes and at different times. Such rights were often conveyed through oral history and not formally documented.

These different ideas of land ownership and tenure are sometimes referred to using different terminology. For example, "formal" or "statutory" land systems refer to ideas of land control more closely affiliated with individual land ownership. "Informal" or "customary" land systems refer to ideas of land control more closely affiliated with land tenure.

Terms dictating control over and use of land can therefore take many forms. Some specific examples of present-day or historic forms of formal and informal land ownership include: