Kaufhaus Isay, Heritage monument in Altstadt-Nord, Germany

Kaufhaus Isay is a five-storey office and commercial building at Zeppelinstraße 4–8, corner of Am Alten Posthof 3, in Cologne's Altstadt-Nord. Built 1911–1913 by Helbig & Klöckner, it has nine window axes on Zeppelinstraße and seven on Am Alten Posthof, with the main entrance centred on Zeppelinstraße and a side entrance at the left end of Am Alten Posthof. The hipped roof originally had four gables on the long side and three on the short side.

The corner plot at Zeppelinstraße and Am Alten Posthof was bought by Gebrüder Isay, a wholesale cloth, wool and knitwear firm founded in 1871, which commissioned Helbig & Klöckner; the building was ready for occupation on 1 April 1913. In 1933 the Jewish-owned firm was converted into the Wistri Gesellschaft für deutsche Wirk- und Strickwaren GmbH and sold below value; ownership of the property passed in 1941 to Ludwig Mengel, Friedrich Ritter, Franz Weiss and Erich Ortloff. Lightly damaged in the war, it was rebuilt and from 1956 to 1958 enlarged by a bay, raised one storey and given a new attic under plans by Wilhelm Riphahn.

The building's name recalls the Gebrüder Isay firm, a wholesale cloth, wool and knitwear business founded in 1871 that commissioned the house and kept its head office here. In 1938 the address sheltered sixteen companies, among them a Deutsche Bank branch, a corset shop and a Telefunken office.

The main entrance still sits in the middle of the Zeppelinstraße facade, with a side entrance at the outer left of Am Alten Posthof. Since the 1956–1958 rebuild the building reads as five storeys from the street but seven towards the courtyard, so the roofline differs by side.

The building survived almost unscathed despite Cologne's severe destruction during World War II, making it one of the few intact early 1900s trading palaces in the city. This rarity makes it an important witness to the commercial architecture of that era.