This is already the fourth edition of our Handbook, and the underlying topic is more pressing then even. As the last editions have appeared, important new research findings on climate change have been gathered and published, yet solid action lacks behind. The evidence of anthropogenic climate change has further solidified, and the detrimental effects and risks of global warming have become more visible. Both mitigation and adaptation of climate change are vital to manage the crisis we are in. The handbook in its presently fourth edition was again extensively updated and extended in coverage. The broader presentation and discussion of adaptation measures offers a maximum benefit to practitioners. The impacts of climate change have made it into our daily lives. All human beings, in turn, can contribute to the mitigation and adaptation of climate change. Consequently, these topics are discussed in schools, in private settings, in research, and in the business world. We can see multiple implications of climate change in our daily lives. The 2020 COVID-19 crisis that has suddenly paralyzed the entire world has been mastered by now. Climate change is slower and subtler than such an epidemic, but even more severe in its potential and factual consequences, where no “fix” like a vaccination exists to return to the previous state. We can repeat what was said previously: This handbook is more necessary than ever before. Over the last several million years, there have been warmer and colder periods on Earth, and the climate fluctuates for a variety of natural reasons, as data from ice cores, tree rings, and pollen samples have shown. However, human presence on Earth—due to number and activities—has reached to such an extent that it can impact the globe in potentially catastrophic ways, in terms of magnitude and irreversibility. Mitigation and adaptation are the two principal routes of our responses to climate change, and they, in fact, can be best achieved collectively by world citizens, scientists, and nonscientists in our daily lives. The “blame” cannot be placed solely on consumers with their individual carbon footprints and choices of “climate friendly” over “less climate friendly” alternatives and the purchase of compensation certificates. Legislators and companies need to provide the framework and product and service offerings which are more sustainable than those in the past decades. We do not need more waste collection and recycling, but a paradigm change in product and packaging design, taking the entire product life cycle into consideration. We do not need to possess individually all types of items, also more than once, that are hardly utilized, but develop innovative approaches for sharing facilities efficiently. We do not need to have more output and sales of materials every consecutive year, but come up with creative business models like materials leasing, where closed loops are realized. Climate change is caused by CO2, and we cannot fully decarbonize. We need to defossilize, converting the feedstock base to biobased, renewable resources, and not only change to less carbon-intense means of energy but also reduce the consumption. We also need to work hard on other greenhouse gases, such as methane, the impact of which has long been underestimated, or hydrogen, which also comes with a greenhouse warming potential (GWP) when being released into the atmosphere—a likely scenario as the industry is being ramped up. What we urgently need is a science-based approach. Not lobbyist arguments, but fact-based decisions. Every single individual can contribute to protecting our climate, with smaller and larger levers. Knowledge is at the beginning, and this is where the Handbook makes its contribution. This chapter is an introduction to climate change and the handbook in its fourth edition. Current state of the arts of climate change mitigation and adaptation approaches are discussed.