Sisley's student works are lost.
His first landscape paintings are sombre, coloured with dark browns, greens, and pale blues.
They were often executed at Marly and Saint-Cloud. Little is known about Sisley's relationship with the paintings of J. M. W. Turner and John Constable, which he may have seen in London, but some have suggested that these artists may have influenced his development as an Impressionist painter, as may have Gustave Courbet and Jean-Baptiste-Camille Corot.
He was inspired by the style and subject matter of previous modern painters Camille Pissarro and Edouard Manet.
Among the Impressionists, Sisley has been overshadowed by Monet, whose work his resembles in style and subject matter, although Sisley's effects are more subdued.
Described by art historian Robert Rosenblum as having "almost a generic character, an impersonal textbook idea of a perfect Impressionist painting", his work strongly invokes atmosphere, and his skies are always impressive.
He concentrated on landscape more consistently than any other Impressionist painter.
Among Sisley's best-known works are Street in Moret and Sand Heaps, both owned by the Art Institute of Chicago, and The Bridge at Moret-sur-Loing, shown at Musée d'Orsay, Paris.
Allée des peupliers de Moret (The Lane of Poplars at Moret) has been stolen three times from the Musée des Beaux-Arts in Nice - once in 1978 when on loan in Marseilles (recovered a few days later in the city's sewers), again in 1998 (when the museum's curator was convicted of the theft and jailed for five years with two accomplices), and finally in August 2007 (on 4 June 2008 French police recovered it and three other stolen paintings from a van in Marseilles).
A large number of fake Sisleys have been discovered.
Sisley produced some 900 oil paintings, some 100 pastels and many other drawings.
During the Nazi period (1933–1945) a number of Sisley works were taken from Jewish art collectors by Nazis or their agents as part of the massive looting of Jews that preceded the Holocaust.
On 18 June 2004 Sisley's Soleil de printemps, le Loing (1892) was restored to the family of Louis Hirsch, in a ceremony in Paris.
In 2008 a dispute erupted between Alain Dreyfus, an art dealer in Switzerland, and the auction house Christie's over a Sisley painting First Day of Spring in Moret, that was claimed by the Lindon family in court in Paris.
Dreyfus said that Christie's had not sufficiently examined the work's history, or provenance, before putting it up for sale.
Also in 2008, the Sisley Bateux en Réparation à Saint Mammès (1885) was recognised as having been looted by the Nazis and the subject of a settlement with the heirs of Benno and Frances Bernstein who had owned it before Nazi occupation.
Numerous Sisleys such as Winter Landscape were known to have been seized by the Nazi looting organisation known as the E.R.R. and still have not been found.
The German Lost Art Foundation has 24 listings for Sisley.