Saint Andrew's Cross refers either to a flag in the form of a white saltire on a blue field or its inverse, a blue saltire on a white field.

Numerous flags of this type are found, mostly historically connected with Scotland or Russia, two of the three countries (along with Greece) of which St Andrew is the patron saint; the design comes from the crux decussata (diagonal cross) upon which Saint Andrew is said to have been martyred. These flags include the national Flag of Scotland, the naval ensign of the Imperial Russian (1696-1917) and Russian navies (1991-present), and the provincial flag of Nova Scotia.

The design of the St Andrew's Cross was also a major inspiration for the Confederate battle flag used during the American Civil War, as described in the article Flags of the Confederate States of America.

St. Andrew's Cross was worn as a badge on hats in Scotland, on the day of the feast of St. Andrew.

The St. Andrew's Cross is also in UK railway signalling as a "cancelling indicator" for the Automatic Warning System or AWS, indicating to the driver the received warning can be disregarded.

The term St Andrew's Cross is often erroneously used for any saltire irrespective of its colours, such as the blue and yellow Saint Alban's Cross, although a true St Andrew's Cross is always blue and white.

References

Ondřejský kříž | Cruz de San Andrés | Croix de saint André | Andráskereszt | セント・アンドリュー・クロス | Krzyż św. Andrzeja | Андреевский крест