The Grassmarket is an historic market square in the Old Town of Edinburgh, Scotland. In relation to the rest of the city the area is a hollow, well below surrounding ground levels.

The Grassmarket is located directly south-east of Edinburgh Castle with the castle dominating views northwards from the space. It adjoins the Cowgate to the east, the West Bow (leading to Victoria Street) to the north-east, King's Stables Road to the north-west and the West Port to the west. Leading off the Grassmarket on its south-west corner is The Vennel, on the east side of which can still be seen some of the best remaining parts of the Flodden and Telfer city walls.

It forms part of the main east-west vehicle arteries through the city centre.

The Grassmarket was, from 1477 to 1911, one of Edinburgh's main markets for horse and cattle. It was also a setting for public executions.

A popular story in Edinburgh is that of Maggie Dickson, a fishwife from Musselburgh who was hanged in the Grassmarket in 1728 for murdering her own baby. After the hanging, her body was taken back to Musselburgh in a coffin. However, on the way there she awoke. Under Scots Law she had served her punishment. Only later were the words "until dead" added to the sentence of hanging. It was also to some extent seen as divine intervention, and so she was allowed to go free. In later life (and legend) she was thereafter referred to as Half-Hangit Maggie. There is now a pub named after Maggie situated on the Grassmarket.