The main objective of this volume of the Cambridge History of Science is to explore modern science using different frames of reference: national, transnational, international, and global. The chapters in the volume primarily analyze the history of modern science during the late-eighteenth, nineteenth, twentieth, and early twenty-first centuries. However, authors were encouraged to explore earlier periods where appropriate, especially when necessary as background. Chapters in Part II of the volume focus on particular national and regional contexts covering all parts of the world.