The term 'sustainable livelihood' was first used as a development concept in the early 1990s. Chambers and Conway (1991) defined a sustainable livelihood as follows: a livelihood comprises people, their capabilities and their means of living, including food, income and assets. Tangible assets are resources and stores, and intangible assets are claims and access. A livelihood is environmentally sustainable when it maintains or enhances the local and global assets in which livelihoods depend, and has net beneficial effects on other livelihoods. A livelihood is socially sustainable which can cope with and recover from stress and shocks, and provide for future generations.; A livelihood is sustainable when it can cope with and recover from stresses and schocks, maintain or enhance its capabilities and assets, while not undermining the natural resource base.