Klaus Töpfer, Executive Director of the Institute for Advanced Sustainability Studies (IASS) in Potsdam, former UN Under-Secretary-General and Executive Director of the UN Environment Programme as well as Minister for the Environment in Germany, turned 75 in 2013. His outstanding achievements inspired us to assemble this volume. Klaus Töpfer has been at the forefront of sustainability efforts for several decades, with a long track record of turning vision into reality, and a firm conviction that knowledge can be a crucial building block for transitions towards sustainability. Our world is shaped, more than ever before, by human activities. The scope of technology, to systemically alter nature in ways impossible for previous generations to comprehend, requests and requires a new relationship with 'planet Earth.' Such a relationship may speak, in the end, not just of profit and loss but also of a new meaning of wealth, including a sense of ethics, stewardship, and responsibility. For the time being, it seems paramount to face these new challenges, striving for new ways of understanding and, subsequently, new modes of response.