Greenlaw is a town and civil parish situated in the foothills of the Lammermuir Hills on Blackadder Water at the junction of the A697 and the A6105 in the Scottish Borders area of Scotland. At the 2001 census, the parish had a population of 661.

Blackadder Water is a river in Berwickshire in the Scottish Borders area of Scotland, forming part of the River Tweed system. It reached 2.84m at Mouthbridge, which was its highest level ever recorded on Tuesday 22 October 2002 at 2:45pm.