Flensburger Brauerei is a brewery located in Flensburg, Schleswig-Holstein, Germany. It was founded in 1888 by five citizens of Flensburg. Today it remains primarily in the hands of the founding families Petersen and Dethleffsen.

Before modern cooling methods, the brewery used blocks of ice from frozen lakes in winter to keep the underground facilities cool in summer. Additionally, it operates its own water well, which is fed by an underground vein of very old melted water from the Ice Age originating from Scandinavia.