Jethou is a small island that is part of the Bailiwick of Guernsey in the Channel Islands. It is privately leased from the Crown, and not open to the public. Resembling the top of a wooded knoll it is immediately south of Herm and covers approximately 44 acres (18 ha).

There is evidence of flint manufacturing in an area exposed only at low water between the island and Crevichon which shows occupation around 4,000 BC. It is said that in AD 709 a storm washed away the strip of land that connected the island with Herm.

The Vikings called the island Keitholm. The island's current name retains the related Norman -hou suffix, meaning small island or small hill.

In 1416, it became part of Henry V's estate and still remains Crown property, now leased to the States of Guernsey.

On the top is a marker. It is said that in earlier times, pirates were hanged on it with chains, as on nearby Crevichon.

At the back (east) of Jethou, puffins can be seen swimming off the rocks.