Portsoken, traditionally referred to with the definite article as the Portsoken, is one of the City of London, England's 25 ancient wards, which are still used for local elections. Historically an extra-mural ward, lying east of the former London Wall, the area is sometimes considered to be part of the East End of London. The ward is about 5 hectares in area.

In everyday speech, the Portsoken, which is mainly oriented north-south, is referred to as Aldgate, this applies especially to the central area where the A11 road becomes known as Aldgate High Street as it passes through the ward.

John Stow's Survey of London records that the "soke" – in this context the right to extract fines as a source of income – (later "liberty") was granted in the time of Saxon king Edgar the Peaceful, east of Aldgate to a guild of knights, the Cnichtengild, in exchange, essentially, for regular jousting. Norman kings confirmed these rights but later the land was voluntarily transferred to the Priory of the Holy Trinity by the descendants of the guild.

In 1120 or 1121 (the exact date is unknown), the Portsoken was granted as a liberty to the Priory of Holy Trinity, which had been founded in 1107 by Queen Matilda, the wife of King Henry I. The sitting prior of Holy Trinity became, ex officio, an alderman of the City of London Corporation representing the Portsoken ward, and remained so until the Dissolution of the Monasteries by King Henry VIII in 1531.

The Ward was originally coterminous with the once slightly larger parish of St Botolph without Aldgate and extended as far south as the Thames. However, the growth of the Tower of London beyond the line of the London Wall, disputes with the Tower, the creation of the Tower Liberty other factors resulted in the southern area being lost to the ward and to the City of London, after around 1200.

The area taken for the Tower Liberty was lost to both the city ward of Portsoken and to the parish, while East Smithfield was lost to the Portsoken but remained a part of the parish. In 1442, St Katharine's (first established in 1147) became an independent Precinct, the Precinct of St Katharine by the Tower and so ceased to be a part of the East Smithfield area of the parish.

In 1332, a tax assessment showed 23 taxpayers in the Portsoken. However, this figure only included freemen of the City of London who possessed moveable property worth more than 10 shillings, and so did not include the poor, non-citizens, or members of religious orders. A later subsidy roll from 1582 showed that the ward's taxpayers had been assessed to pay a total of 57 pounds, 11 shillings and 4 pence.

The Portsoken has long had a mixed population, and in 1483 is recorded as having more aliens in its population than any ward in the City of London.