The Dornoch Firth is a firth on the east coast of Highland, in northern Scotland. It forms part of the boundary between Ross and Cromarty, to the south, and Sutherland, to the north. The firth is designated as a national scenic area, one of 40 such areas in Scotland. The national scenic area covers 15,782 ha in total, of which 4,240 ha is the marine area of the firth below low tide. A review of the national scenic areas by Scottish Natural Heritage in 2010 commented:By comparison with other east coast firths the Dornoch Firth is narrow and sinuous, yet it exhibits within its compass a surprising variety of landscapes. It is enclosed by abrupt rounded granitic hills clad in heather moor and scree, their Gaelic names of cnoc, meall and creag giving the clue to their character. Their lower slopes are frequently wooded, oakwoods being a noticeable feature of the area, but with other deciduous and coniferous species represented in plantations which vary from the policy plantings of Skibo Castle to the pines of the Struie Forest.

Firth is a word in the English and Scots languages used to denote various coastal waters in the United Kingdom, predominantly within Scotland. In the Northern Isles, it more often refers to a smaller inlet. It is linguistically cognate to fjord, which has a more constrained sense in English. Bodies of water named "firths" tend to be more common on the Scottish east coast, or in the southwest of the country, although the Firth of Clyde is an exception to this. The Highland coast contains numerous estuaries, straits, and inlets of a similar kind, but not called "firth" ; instead, these are often called sea lochs. Before about 1850, the spelling "Frith" was more common.