At the 1948 "Salon des Réalistes Nouvelles" in Paris, Geiger's first abstract painting was exhibited. One year later, together with Baumeister, Matschinsky-Denninghoff and Winter he founded the group "ZEN 49".
During the 1950s, Geiger developed non-representational colour spaces, in which from 1957 shapes are silhouetted against a nearly monochrome, only lightly sculpted plane. In the 1960s, red and blue become the dominating colours of large format paintings.
From 1967 on, the shape of the compressed circle dominates Geiger's paintings, by the mid-1970s that is replaced by bright, seemingly disembodied rectangles. During the 1980s the colour red is varied with all the possibilities and polarities of the appliance of colour to the canvas. The 1990s are characterized by paintings in unusual formats with manifold combinations of geometric shapes.
