The Natisone (Latin: Natiso; Friulian: Nadison; ) is a river in Slovenia and Italy. It flows for some time as a border river between Slovenia and Italy, continues in Slovenia and then crosses the border and continues in Eastern Friuli, in northeastern Italy. It is the main tributary of the Torre and a sub-affluent of the Isonzo. It has the pluvio-nival regime and belongs to the Adriatic Sea Basin.