Since the 1940s, Kelly has been exploring the possibilities of abstraction. The relationship of form and space is at the core of his art. With his Hard-Edge Painting, he is one of the great Modernists of the American post-war generation. However, he always emphasised that his fundamental abstraction is founded in the world in which we live, in the forms that surround us and in the shadows and spaces between the things: "Since birth we get accustomed to seeing and thinking at the same time. But I think that if you can turn off the mind and look at things only with your eyes, ultimately everything becomes abstract".
Kelly's works have been shown in large exhibitions, for instance at the Museum of Modern Art, the Whitney Museum and the Guggenheim Museum, all in New York, and they are included in the collections of numerous international museums such as that of the Centre Pompidou in Paris, the Museo Nacional Centro de Arte Reina Sofia in Madrid the Tate Modern in London.
