Southend-on-Sea ( (listen)), commonly referred to as Southend (), is a coastal city and unitary authority area with borough status in southeastern Essex, England. It lies on the north side of the Thames Estuary, 40 miles (64 km) east of central London. It is bordered to the north by Rochford and to the west by Castle Point. It is home to the longest pleasure pier in the world, Southend Pier. London Southend Airport is located north of the city centre.

Southend-on-Sea originally consisted of a few poor fishermen's huts and farms at the southern end of the village of Prittlewell. In the 1790s, the first buildings around what was to become the High Street of Southend were completed. In the 19th century, Southend's status of a seaside resort grew after a visit from Princess Caroline of Brunswick, and Southend Pier was constructed. From the 1960s onwards, the city declined as a holiday destination. Southend redeveloped itself as the home of the Access credit card, due to its having one of the UK's first electronic telephone exchanges. After the 1960s, much of the city centre was developed for commerce and retail, and many original structures were lost to redevelopment. An annual seafront airshow, which started in 1986 and featured a flypast by Concorde, used to take place each May until 2012.

On 18 October 2021, it was announced that Southend would be granted city status, as a memorial to the Member of Parliament for Southend West, Sir David Amess, a long-time supporter of city status for the borough, who was fatally stabbed on 15 October 2021. Southend was granted city status by letters patent dated 26 January 2022. On 1 March 2022, the letters patent were presented to Southend Borough Council by Charles, Prince of Wales.

Keddies was a small chain of department stores in Essex, England, with its flagship store in a prime location in Southend High Street (originally called the Broadway). The business had a national reputation, being recognised in The Fashion Handbook and appearing on the side of a Matchbox model 17C bus. Keddies closed for business on 26 February 1996 after going into administration.