Jens Thiis (1870–1942) was a Norwegian art historian, conservator and a prominent museum director. He was conservator at Nordenfjeldske Kunstindustrimuseum (Museum of Arts and Crafts) in Trondheim 1895 and director at Nasjonalgalleriet (The National Gallery) in Oslo 1908–1941.He was unusual alert to tendencies of his time. When at Nordenfjeldske Kunstindustrimuseum in Trondheim he engaged in 1907 Henry van de Velde, now considered one of the foremost style formers in his time, to design a room and all its furniture and furnishings in the museum to display an Art Nouveau interior. He was awarded honorary citizenship of Florence for his works on Florentine Renaissance.The Henry van de Velde-room is unique in its kind being specially designed for this purpose. It has later been recreated in the premises of the new Nordenfjeldske Kunstindustrimuseum. When director, he bought French contemporary art, Monet among others, and thus made a solid base for the French collection in Nasjonalgalleriet, today being one of its main attractions.He is the father of Ragna Stang and Helge Thiis.