The River Esk is a river which flows through Midlothian and East Lothian, Scotland.
It initially runs as two separate rivers, the North Esk and the South Esk.
The North Esk rises in the North Esk Reservoir in the Pentland Hills, in Midlothian, a mile (1½ km) north of the village of Carlops. It flows north-east past Penicuik, Auchendinny, through Roslin Glen, past Hawthornden Castle, Polton, Lasswade and Melville Castle.
The South Esk rises at the southernmost extremity of Midlothian, on the western slopes of Blackhope Scar (the highest of the Moorfoot Hills). It flows north through Gladhouse Reservoir and Rosebery Reservoir, and through the village of Temple, Midlothian, before receiving the Redside Burn close to Arniston House. It is joined by the Gore Water and then the Dalhousie Burn, just to the west of Newtongrange, before passing Newbattle Abbey and proceeding through Dalkeith.
The rivers converge just about 1¼ miles (2 km) north-east of Dalkeith at the edge of the grounds of Dalkeith Palace. From here the River Esk continues north for about 4⅓ miles (7 km), flowing into the Firth of Forth at Musselburgh, East Lothian.