The Australian Soil Classification provides a framework for organising knowledge about Australian soils. It provides a means of communication among scientists and land managers. It is a general-purpose scheme that allocates soils to classes via a key. Classification is a basic requirement of all science and needs to be periodically revised as knowledge increases. This Second Edition includes updates from a working group of the National Committee on Soils and Terrain (NCST), especially in regards to new knowledge about acid sulfate soils (sulfidic materials).