A portcullis is a grille or gate made of wood, metal or a combination of the two.

Portcullises fortified the entrances to many medieval castles, acting as a last line of defence during time of attack or siege. Each portcullis was mounted in vertical grooves in castle walls and could be raised or lowered quickly by means of chains or ropes attached to an internal winch. There would often be two portcullises to the main entrance. The one closest to the inside would be closed first and then the one furthest away. This was used to trap the enemy and often, burning wood or hot oil would be poored onto them from the roof.

The portcullis often appears as a device or emblem in heraldry, such as that employed as the symbol for the Palace of Westminster in London. One example of where a portcullis is found is on a one pence coin, and another on the Canada Customs crest.