He was never closely aligned with any movement and was too retiring in his manner to be the object of a personality cult, like his compatriot Picasso, but the formal and technical innovations that he sustained over a very long career guaranteed his influence on 20th-century art. A pre-eminent figure in the history of abstraction and an important example to several generations of artists around the world, he remained profoundly attached to the specific circumstances and environment that shaped his art in his early years. An acute balance of sophistication and innocence and a deeply rooted conviction about the relationship between art and nature lie behind all his work and account in good measure for the wide appeal that his art has continued to exercise across many of the usual barriers of style.

From Grove Dictionary of Art