Bayernfenster, Leadlight windows in Cologne Cathedral, Germany.

The Bayernfenster are five large stained glass windows positioned along the southern aisle of Cologne Cathedral featuring biblical scenes. They stretch along the side passage and display religious content through intricate colored glasswork.

The idea for the windows came from Sulpiz Boisserée in 1842; King Ludwig I of Bavaria funded them as a gift. They were made between 1846 and 1848 at the Royal Glass Painting Institute in Munich after designs by Heinrich Maria von Hess, painted by Joseph Anton Fischer and Franz Hellweger under Max Emanuel Ainmiller. They were unveiled on 14–15 August 1848 for the cathedral's 600th foundation anniversary. Damaged in bombing raids, they were removed, restored from 1975 to 1983 and reinstalled in 1980.

The five windows read west to east from John the Baptist to Saint Stephen, the first Christian martyr. Their Munich painting style, closer to oil painting than medieval mosaic, drew criticism from Neo-Gothic contemporaries; Karl Christian Andreae wrote in 1879 that they looked like transparent pictures on oil paper.

The windows are visible during regular cathedral opening hours and are easily accessible along the side passage. Natural light changes their color display throughout the day, so visiting at different times offers different views.

Each of the five windows tells a different biblical story, and together they form a series that combines religious teaching with the building's structure. This thoughtful arrangement makes them much more than mere decorative pieces.