Book excerpt: Clay Sedimentology is a comprehensive textbook divided into six parts: - clay minerals and weathering - clay sedimentation on land - origin and behaviour of clay minerals and associated minerals in transitional environments (estuaries, deltas) and shallow-sea environments - diverse origins of clay in the marine environment - post-sedimentary processes intervening during early and late diagenesis - use of clay stratigraphic data for the reconstruction of past climate, marine circulation, tectonics, and other paleogeographical aspects. A basic idea on most topics dealing with sedimentary clays is presented and controversial data and uncertainties from the frontiers of knowledge are discussed.