HMS Monmouth was the sixth "Duke"-class Type 23 frigate of the Royal Navy. She was the seventh ship to bear the name and was launched by Lady Eaton in 1991, being commissioned two years later.

The Type 23 frigate or Duke class is a class of frigates built for the United Kingdom's Royal Navy. The ships are named after British Dukes, thus leading to the class being commonly known as the Duke class. The first Type 23, HMS Norfolk, was commissioned in 1989, and the sixteenth, HMS St Albans was commissioned in June 2002. They form the core of the Royal Navy's destroyer and frigate fleet and serve alongside the Type 45 destroyers. They were designed for anti-submarine warfare, but have been used for a range of uses. Ten Type 23 frigates remain in service with the Royal Navy, with three vessels having been sold to the Chilean Navy, one being retired in 2021, and two being retired in 2023.