This comprehensive account examines the Quaternary critically largely from the point of view of its subdivision, correlation and classification; the approach, therefore, is basically stratigraphical, distinguishing carefully between the different concepts involved in multiple classification. One of the principles of the Quaternary is the bewildering number of existing models, a situation which leaves most students in a state of confusion. Despite an inadequate basis many of the models continue to be used. These are criticised, and more realistic approaches (based largely on the work of the last ten years or so) are outlined