Au is a municipality in the Wahlkreis (constituency) of Rheintal in the canton of St. Gallen in Switzerland.

[3] The blazon of the municipal coat of arms is Azure a Crescent Or in bend issuant behind a Cliff Argent.

Of the rest of the land, 47.8% is settled (buildings or roads) and the remainder (5.9%) is non-productive (rivers or lakes).

[5] The municipality was part of the Unterrheintal district until the creation of the Rheintal Wahlkreis.

Of the foreign population, (as of 2000[update]), 192 are from Germany, 398 are from Italy, 580 are from ex-Yugoslavia, 334 are from Austria, 121 are from Turkey, and 307 are from another country.

[8] The age distribution, as of 2000[update], in Au is: 750 children or 11.7% of the population are between 0 and 9 years old and 792 teenagers or 12.4% are between 10 and 19.

[5] Out of the total population in Au, as of 2000[update], the highest education level completed by 1,459 people (22.8% of the population) was Primary, while 2,500 (39.0%) have completed Secondary, 683 (10.7%) have attended a Tertiary school, and 243 (3.8%) are not in school.

[11] From the 2000 census[update], 3,589 or 56.0% are Roman Catholic, while 1,406 or 21.9% belonged to the Swiss Reformed Church.