The Herdwick is a breed of domestic sheep native to the Lake District in North West England. The name "Herdwick" is derived from the Old Norse herdvyck, meaning sheep pasture. Though low in lambing capacity and perceived wool quality when compared to more common commercial breeds, Herdwicks are prized for their robust health, their ability to live solely on forage, and their tendency to be territorial and not to stray over the difficult upland terrain of the Lake District. It is considered that up to 99% of all Herdwick sheep are commercially farmed in the central and western Lake District.

The wool of a Herdwick has unique qualities relating to durability. Thick bristle type fibres will often protrude from garments made from the wool, forming a protective layer in blizzards—most likely the same qualities that protect the sheep in similar conditions. Herdwicks have been known to survive under a blanket of snow for three days while eating their own wool.

Severely threatened by the 2001 outbreak of foot-and-mouth disease in England and Wales, the breed has survived due to the intent to preserve this unique animal as a crucial part of traditional Lakeland agriculture. Still far fewer in number than most commercial breeds, Herdwicks survive largely due to farming subsidies.