This Outlook presents some stark choices for human societies. On one hand it warns that the diversity of living things on the planet continues to be eroded as a result of human activities. The pressures driving the loss of biodiversity show few signs of easing, and in some cases are escalating. The consequences of current trends are much worse than previously thought, and place in doubt the continued provision of vital ecosystem services. The poor stand to suffer disproportionately from potentially catastrophic changes to ecosystems in coming decades, but ultimately all societies stand to lose. On the other hand, the Outlook offers a message of hope. The options for addressing the crisis are wider than was apparent in earlier studies. Determined action to conserve biodiversity and use it sustainably will reap rich rewards. It will benefit people in many ways - through better health, greater food security and less poverty. It will safeguard the variety of nature, an objective justified in its own right according to a range of belief systems and moral codes. It will help to slow climate change by enabling ecosystems to absorb and store more carbon; and it will help people adapt to climate change by adding resilience to ecosystems and making them less vulnerable.