The Rhenish Expressionists were a loose constellation around the painter August Macke, working in Bonn and Cologne in the years before the First World War. Macke's pictures look at first glance unthreatening — bright fields, women in front of hat shops, a tightrope walker in 1914 — but the colours are saturated past plausibility and the figures move in flat planes, as if the painter has decided perspective is something to be argued with. Macke himself was killed in action in France in September 1914, two months into the war, aged 27. The Kunstmuseum holds the most important collection of his work and of the wider Rhenish Expressionist circle anywhere in the world. The museum places Macke deliberately next to Robert Delaunay, the French painter whose simultaneous-contrast experiments had so reshaped his thinking on a 1912 visit to Paris.

The other floor of the permanent collection moves into what postwar German artists did with the catastrophe. Joseph Beuys, with his felt and fat and slogans about social sculpture. Georg Baselitz, painting his figures upside down. Anselm Kiefer, dragging the iconography of myth and Nazi memory back into the studio. Hanne Darboven's obsessive counted sheets of numbers. Blinky Palermo's quiet monochromes, hung — in a curatorial move the museum likes — alongside the British land artist Richard Long. Wolf Vostell's video and Fluxus pieces. The Italian Arte Povera artist Jannis Kounellis turns up next to Gerhard Merz; Lucio Fontana keeps company with Beuys. The Kunstmuseum's three strong points, in its own description, are Rhenish Expressionism, postwar German art from the 1960s into the early 1990s, and a major international collection of postwar prints — about 5,000 sheets, including Beuys's so-called multiples and books illustrated by Max Ernst.

Since 1984 Bonn has been the home of the Videonale, a biennial festival of contemporary video art, and since 2005 the festival has lived inside the Kunstmuseum's walls. The museum's own Oppenheim Collection of video work includes pieces by Dennis Oppenheim himself, Joan Jonas, Klaus vom Bruch, Marcel Odenbach, and Julian Rosefeldt — work that runs on monitors, projectors, or full darkened rooms. Schultes's 1992 building was conceived around exactly this kind of programming: 4,000 square metres of exhibition area, three entrances, and a light system that the architect treated as a curatorial collaborator rather than a service. It was a 100-million-Deutsche-Mark gamble, expensive enough at the time to be controversial. Three decades later the building is widely understood as one of the most successful museum architectures of the Bonn Republic.

Not everything has been comfortable. In 2005 the museum sold the former Grothe Collection — a long-term loan turned permanent transfer — to the collectors Sylvia and Ulrich Ströher for 50 million euros. The decision was controversial in the way Germany's museum world has of being controversial: quiet, principled, and slow-burning. The works that left included Sigmar Polke's Degenerate Art series and Gotthard Graubner's Assisi Cycle. Their departure cleared wall space for what the incoming director Stephan Berg called a 'certain rejuvenation' from 2007 — more recent painters, more video, more installation. Some of the sculptures in the forecourt also went to the Ströhers. The collection that remains is leaner and younger, still anchored to Macke and Beuys but with a sharper sense that the museum of modern art also has to be a museum of art being made now.