White Mountains Re Sirius (Sirius) is a Swedish-based international reinsurer that focuses mainly on property and other short-tailed lines. WMRe Sirius is the largest reinsurance company in Scandinavia and a leading reinsurer in Europe.

Sirius is rated "A" (Excellent) by A.M. Best, "A-" (Strong) by S&P, "A3" (Good) by Moody's.