The Swan Upping is the annual census of the swan population living on the stretches of the River Thames between Sunbury Lock and Abingdon Bridge, which occurs in the third week in July. The ceremony originates from the 12th century, when the Crown claimed ownership of the swans, and wished to check their numbers, as swan meat was then regarded as a freely available luxury food item.

The swan upping is organised by The Queen's Swan Marker who has the responsibility of looking after The Queen's swans all year round. The birds are examined for beak marks which distinguish the unmarked royal swans from the beak nicks of the ancient Vintners and Dyers birds, who were granted swan ownership rights in the 15th century, and are the only survivors of the various bodies formerly entitled to swan rights on the River Thames.

The Upping takes place during the Third week of July. The Swan Marker and Swan Uppers, accompanied by their opposite numbers from the Vintners' and Dyers' Livery Companies use traditional rowing skiffs to make the five day journey from Sunbury upstream to Abingdon. The member of the various guild and royal bodies all wear different uniforms. The Swan Marker wears a scarlet jacket with his badge of office on the sleeve, and each of the teams of uppers are denoted by different coloured coats. Each skiff also flies the appropriate flags and pennants, with The Queen's boats bearing a white flag depicting the royal crown and cypher.

The name 'Swan Upping', occasionally known as Swan Hopping, comes from the traditional shout of 'all up', given when someone spots a swan brood - this warns all the boats to get into position to catch the swans. After they are caught, the cygnets are weighed and measured to obtain estimates of growth rates, and all the birds are examined for any sign of injury by the Queens Swan Warden, currently Professor Christopher Perrins of Oxford University, who also rings the cygnets with a unique identification number then sets them free.