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.

The Royal Navy (RN) is the naval warfare force of the United Kingdom, British Overseas Territories and Crown Dependencies, and a component of His Majesty's Naval Service. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against France. The modern Royal Navy traces its origins to the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.