In the 21st century, the world is faced with threats of global scale that cannot be confronted without collective action. Although global government as such does not exist, formal and informal institutions, practices, and initiatives—together forming “global governance”—bring a greater measure of predictability, stability, and order to trans-border issues than might be expected. Yet, there are significant gaps between many current global problems and available solutions. Thomas G. Weiss and Ramesh Thakur analyze the UN's role in addressing such knowledge, normative, policy, institutional, and compliance lapses. The UN's relationship to these five global governance gaps is explored through case studies of some of the most burning problems of our age, including terrorism, nuclear proliferation, humanitarian crises, development aid, climate change, human rights, and HIV/AIDS.