This chapter discusses the work carried out to establish the link between climate and atmospheric composition over the last million years, a period over which archives from different media offer precious information with a high degree of detail and accuracy. It examines how glacial archives and marine and continental sediments were used to reconstruct the changes in the atmospheric composition and biogeochemistry of the climate system over the last million years. It then looks at the major biogeochemical cycles and shows how one can explain the changes. It also points out some of the key questions that remain unanswered. © 2014 Elsevier Ltd. All rights reserved.