It is well known that arid-land soils are adversely affected by the presence of sodium, yet only recently has the behaviour of sodium in the soils of humid and sub-humid areas, where most of the world's cereal crop is grown, been recognized. This book of commissioned chapters will focus on the `non-classic' sodic soils, describing the processes of soil degradation resulting from sodium and other deleterious components (such as magnesium), and outlining strategies for ameliorating their effects on soil systems.