Herm is the smallest of the Channel Islands and is part of the Baliwick of Guernsey and not-technically a part of the United Kingdom. Herm is only 1½ miles long and less than half a mile wide. It is oriented so that its greatest length runs north-south. The northern half of the coastline is surrounded by sandy beaches, the southern half is rocky. Shell Beach and Belvoir Bay are two of the major tourist attractions. The isle of Jethou is just to the south. It is said that in 709 AD a storm washed away the strip of land which connected the island with Herm. To the west is Little Roussell (Petit Ruau)and to the east is Big Roussel (Grand Ruau) and Sark. Much of Herm's bedrock is granite.

Herm was occupied in prehistoric times; the remains of Neolithic chamber tombs have been found on the island. The first records of Herm's inhabitants in historic times are from the 6th Century, when the island became a centre of monastic activity; the name 'Herm' supposedly derives from hermit monks who settled there. The most important moment in Herm's political history was 933, when the Channel Islands were annexed to the Duchy of Normandy. After the annexation, Herm gradually lost its monastic inhabitants, and between 1570 and 1737 it was used as a hunting ground by the governors of Guernsey.

In the late 18th century, industry arrived in Herm with the establishment of granitequarries to serve the large scale military fortifications undertaken in the islands. The island was let to tenants by the Crown and was generally off-limits to visitors.

Between 1920 and 1923, the noted Scottish writer founder of the Scottish National Party, Compton MacKenzie was tenant of the island.

On 25 July, 1940, a few weeks after the arrival of German troops in Guernsey and Jersey, nine German soldiers landed on the island in a commandeered motor boat to shoot a propaganda film. They went back to Guernsey the same day. Herm's sandy beaches were soon used for practising landings from barges, in preparation for the invasion of England, but otherwise the island saw little of the Germans beyond officers making trips to shoot rabbits. In a British nighttime raid on the island in February 1943, commandos wandered around the island without finding any signs of life at all, let alone enemy troops. Herm was spared the huge concrete blockhouses, anti-tank walls and observation towers that were to disfigure the larger islands.

After the war, the Statews of Guernsey decided to buy Herm from the Crown in order that its pleasant atmosphere could be enjoyed by Guernsey residents. The States now rent the island to a tenant, who is expected to maintain the island for the benefit of its visitors.

The most influential tenant has been Major Peter Wood, who looked after the island from 1949 to 1980, after which Adrian and Pennie Wood Heyworth, took over. Major Wood died in 1998.

On 17 May, 2008 that the tenants had put the remaining 40 years of their lease up for sale, with an asking price of £15,000,000. In September 2008 it was announced that Starboard Settlement, a trust, had acquired the remainder of the lease for considerably less than the asking price.The trust formed a Guernsey company, Herm Island Ltd, to manage the island for the trustees.