A person or community's rights to land and other natural resources defines their natural resource tenure. Legally, tenure is a bundle of both rights and obligations: the rights to own, hold, manage, transfer, or exploit resources and land, but also the obligation not to use these in a way that harms others (Bruce 1998a:1; FAO 2002:10). In other words, tenure defines property and what a person or group can do with it—their property rights.

However, tenure is not only a legal concept but a complex social institution, often involving traditional practices and customary authorities as much as formal laws. It governs ownership and access to natural resources, which is the gateway to use and benefit from these resources. As such, tenure is at the heart of the poor's ability to derive income and subsistence from ecosystems—to make them part of a sufficient and sustainable livelihood. (See Box 3.1 Understanding the scope of resource tenure.)

In many parts of the world today, resource tenure systems and property rights regimes are undergoing an important evolution. Fundamental shifts are occurring in the way that people and institutions think about the ownership of land, water, forests, fisheries, and other natural assets—about who controls these assets, who benefits from them, and where the power to make decisions about them is vested.

Two countervailing global trends in the evolution of resource tenure are evident. One trend stems from globalization. The growing economic integration of nations and societies has increased the sphere of private property and private responsibility, with government assuming a lesser role with respect to the private sector and civil society. This has important implications for how public lands and natural resources—often common pool resources—are managed, with more power over resources transferred to corporate interests through privatization or the granting of resource concessions (Johnson et al. 2001).

At the same time, there is a trend toward decentralization of natural resource management. Local and community-level institutions have become more assertive in the management of local resources, and this decentralized approach also has important implications for resource tenure. Indigenous groups have, for example, been more vigorous in pressing their ancestral claims to lands they inhabit but to which they lack formal title.

These two trends are shaping—and promise to profoundly transform—the capacity of the poor to earn environmental income from natural resources. For example, as illustrated in a study on the impact of globalization on the implementation of community-based natural resources management (CBNRM) in the Philippines, these global trends have the potential to both undermine and strengthen governance conditions that benefit the poor (La Viña 2002:24). Growing economic integration through increased trade and the emergence of multilateral environmental agreements, such those as on climate change and biodiversity, pose both threats and opportunities for poor communities worldwide.

The significance for the poor of changes in resource tenure systems and property rights systems is not limited to their economic impacts. For many rural communities, resource tenure is a central social institution that governs not only their relationship to the land and natural resources but also the relationships between families, between members of the community and those outside it, and between villages, communities, and peoples. Therefore, changes in tenure and property regimes have implications for the entire social fabric of rural communities. This is true for all tenure and property systems relevant to natural resources, but is particularly evident in the evolution of land tenure.