The science is clear: climate change is happening, and it is linked directly to human activities that emit greenhouse gases. This overview summarizes the six-part series Climate Change 101: Understanding and Responding to Global Climate Change. Science and Impacts discusses the most current scientific evidence for climate change and explains its causes and projected impacts. As explored here and in greater depth in Technological Solutions, a number of technological options exist to avert dangerous climatic change by dramatically reducing greenhouse gas emissions both now and into the future. Business Solutions, International Action, State Action, and Local Action describe how business and government leaders at all levels have recognized both the challenge and the vast opportunity climate change presents. These leaders are responding with a broad spectrum of innovative solutions. To successfully address the enormous challenge of climate change, new approaches are needed at the international level, and the United States must re-engage in the global effort and adopt strong and effective national policies.