Environmental history is the study of human interactions with nature over time. The book presents - through three paths, placed in a global perspective (analysis of transformation factors; evolution of ecological reflections; trajectories of environmentalism) - an analysis of the complex change caused by human activities. The study focuses on the twentieth century and the first twenty years of the twenty-first century, that is the historical time during which the scale of environmental problems reached such a size as to create a widespread alarm for the survival of homo sapiens on Earth.