When the Brundtland Commission offered its famous definition of sustainable development–“to meet the needs of the present without compromising the ability of future generations to meet their own needs”–it presented many challenges to policymakers. Not least among these is the question of how we measure progress towards sustainable development. Without indicators to guide policy, commitments to achieving sustainability risk being no more than fine words on paper. Since the time of the Brundtland Commission there has been a worldwide effort to ...