The Southern Indiana Athletic Conference (SIAC) is a high school athletic conference based in Evansville, Indiana.

Mater Dei and Memorial are private Catholic high schools run by the Roman Catholic Diocese of Evansville, and the largest member is Castle, a public school located in neighboring Newburgh in Warrick County under the Warrick County School Corporation.

The league was founded in 1936, and at one point stretched far across southern and western Indiana: from Mount Vernon in the west to New Albany in the east, and from Evansville in the south to Terre Haute in the north.

Jasper and Vincennes Lincoln announced in May 2019 that they would leave the disbanding Big Eight Conference to rejoin the Southern Indiana Athletic Conference beginning with the 2020–21 season.

Vincennes Lincoln announced in January 2025, that it will depart the SIAC for the Western Indiana Conference after the 2025-26 season, citing lack of ability to compete with the Evansville schools, setting off a possible search for a replacement which may involve schools like Heritage Hills and Gibson Southern of the Pocket Athletic Conference None * = indicates title won before IHSAA State Tournament was initiated * = indicates title won before IHSAA State Tournament was initiated + = indicates title sanctioned by the Indiana High School Bowling Association * = indicates title won before IHSAA State Tournament was initiated