The Pentland Firth, which is actually more like a strait than a firth, separates the Orkney Islands from the northern tip of the Scottish Highland region around Caithness.

On the southern (Caithness) shore is the town of Thurso, the port of Scrabster, the famous John o' Groats, Mey (site of the Castle of Mey), along with many smaller villages. The headland of Dunnet Head protrudes into the Pentland Firth and its most northly point, Easter Head, is also that of mainland Britain.

In the middle of the Pentland Firth are two significant islands, Stroma and Swona, with the small Pentland Skerries group in the east. The islands of Hoy and South Ronaldsay border the firth to the north and are part of the Orkney Islands.

One ferry runs from Scrabster in Caithness to Stromness on the Orkney Mainland, running along the western fringes of the Pentland Firth, while another runs from Gills Bay near John o' Groats to St Margaret's Hope on South Ronaldsay. In the summer months a passenger only ferry runs from John o'Groats to Burwick on South Ronaldsay.