This thesis explores the role of private sector social entrepreneurship in sustainable development in New Zealand. A review of literature reveals sustainable development to be a diverse, complex, and challenging concept, encompassing issues from rhetorical ambiguity to the accelerating deterioration and uncertainty in natural and social systems. While business is commonly seen to exacerbate many of the challenges associated with sustainable development, this research suggests that business, as it is utilised by social entrepreneurs to spur positive change, may be a powerful tool for achieving sustainability. Three cases of private sector social entrepreneurship in New Zealand are documented by this research, drawn from the coffee roasting, still bottled water, and film and media industries. The cases are used to elucidate the relationships that exist between the two phenomena within the thematic areas of conceptualisations of sustainable development, motivations and business, and change. The entrepreneurs in this research each demonstrate qualities consistent with assertions in the literature in that they desire to affect change, they are innovative, and that their pursuits are characterised by the creation of new value. These entrepreneurs expectedly contrast with many of their industry counterparts in their recognition of opportunities amidst threat or tragedy, their desires to benefit society in some way, and in their use of business to affect positive change. However, this research also offers new knowledge regarding the role of social entrepreneurship in sustainable development through explicating the ways in which the entrepreneurs each conceptualise sustainable development. Furthermore the entrepreneurs unanimously observe that achieving sustainable development necessitates both incremental and fundamental approaches to change. Also of emergent significance are the roles adopted by the entrepreneurs in education and in raising awareness towards catalysing changes in the ways we live, think and behave. Taken together, as agents of change, social entrepreneurs present much hope and promise in realising a more sustainable world.