During the past decades, the worldwide spread of the human immuno-deficiency virus (HIV) has created one of the deadliest epidemics in history. In 2006, a total of 39.5 million people were living with HIV. Sub-Saharan Africa is clearly the most affected area of the world with more than 24...

The destruction of the Amazon is a major global environmental issue, not only because of greenhouse gas emissions or direct impacts on biodiversity and livelihoods, but also due to the forest’s role as a tipping element of the Earth System. It means that after crossing a biophysical threshold,...

The phenomenon of collective action and the origin of collective action problems have been extensively and systematically studied in the social sciences. Yet, while we have substantial knowledge about the factors promoting collective action at the local level, we know far less about how these...