The anonymous master who painted this work was the leading painter in Cologne shortly after 1400. His name derives from his finest work, Saint Veronica with the Sudarium, preserved in the Alte Pinakothek, Munich. In this Crucifixion the attenuated boneless figures, the sinuous contours of the drapery folds, and the delicate colors set off against the gold ground are all hallmarks of the International Gothic style. The subject is Christ's suffering and death on the cross and the grief of the weeping Virgin Mary and Saint John the Evangelist; yet, the sorrow of the event is softened by the figures' gentle expressions. Even the tiny angels who catch the blood flowing from Christ's wounds add a decorative and fanciful touch.
The painting was probably used as a focus for prayers and meditation by a Carthusian monk, since a member of that monastic order is shown kneeling at the right of the cross. The painting's small size would make it suitable for such use, probably in the monk's cell.
Cologne was the largest and most densely populated city in Germany at the end of the Middle Ages. It supported a wealthy middle class and many religious institutions, including the Charterhouse of Saint Barbara, for which this Crucifixion may have been painted.
More information on this painting can be found in the Gallery publication German Paintings of the Fifteenth through Seventeenth Centuries, which is available as a free PDF https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/german-painting-fifteenth-through-seventeenth-centuries.pdf