Along with Mary Cassatt and John Henry Twachtman, Hassam was instrumental in promulgating Impressionism to American collectors, dealers, and museums.

He also began to add a crescent symbol in front of his signature, the meaning of which remains speculative,[9] possibly an allusion to his penchant for implying Middle Eastern or Turkish origins.

They traveled throughout the United Kingdom, the Netherlands, France, Italy, Switzerland, and Spain, studying the Old Masters together and creating watercolors of the European countryside.

He also joined the "Paint and Clay Club", expanding his contacts in the art community, which included prominent critics and "the readiest and smartest of our younger generation of artists, illustrators, sculptors, and decorators—the nearest thing to Bohemia that Boston can boast.

"[10] Friends found him to be energetic, robust, outgoing, and unassuming, capable of self-mockery and considerate acts, but he could be argumentative and wickedly witty against those in the art community who opposed him.

[11] Hassam was particularly influenced by the circle of William Morris Hunt, who like the great French landscape painter Jean-Baptiste-Camille Corot, emphasized the Barbizon tradition of working directly from nature.

"[10] In 1885, a noted critic, in part responding to Hassam's early oil painting A Back Road (1884), stated that "the Boston taste for landscape painting, founded on this sound French school, is the one vital, positive, productive, and distinctive tendency among our artists today...the truth is poetry enough for these radicals of the new school.

Forget the Beaux-Arts and the models and render the intense life which surrounds you and be assured that the Brooklyn Bridge is worth the Colosseum of Rome and that modern America is as fine as the bric-a-brac of antiquity.

[16] He took advantage of the formal drawing classes with Gustave Boulanger and Jules Joseph Lefebvre, but quickly moved on to self-study, finding that "[t]he Julian academy is the personification of routine...[academic training] crushes all originality out of growing men.

He sent these works back to Boston and their sale, combined with that of older watercolors, provided him with sufficient income to sustain his stay abroad.

In this dramatic change of technique, he was laying softer, more diffuse colors to canvas, similar to the French Impressionists, creating scenes full of light, done with freer brush strokes.

His closest contact with a French Impressionist artist occurred when Hassam took over Renoir's former studio and found some of the painter's oil sketches left behind.

[23] It skillfully uses a distinctive dark palette of blacks and browns (normally considered "forbidden colors" by strict Impressionists) to create a winter urban panorama, which Le Figaro praised for its "American character".

During his European stay, he continued to favor street and horse scenes, avoiding some of the other favorite depictions of the Impressionists, such as opera, cabaret, theater, and boating.

Hassam enthusiastically painted the genteel urban atmosphere of New York that he encountered within walking distance of his apartment, and avoided the squalor of the lower-class neighborhoods.

To compensate, Hassam would find a suitable location, make sketches of the components of his planned painting, then return to the studio to construct a total impression that was actually a composite of smaller scenes.

[31] During the summers, he would work in a more typical Impressionist location, such as Appledore Island, the largest of the Isles of Shoals off New Hampshire, then famous for its artist colony.

"[32] Hassam's subjects for his paintings included Thaxter's flower garden, the rocky landscape, and some interior scenes rendered with his most impressionistic brush strokes to date.

[34] After a trip to Havana, Cuba, Hassam returned to New York and had his first major one-man auction show at the American Art Galleries in 1896, which featured over 200 works that spanned his entire career to date.

After a brief period of depression and drinking as part of an apparent mid-life crisis, the forty-five-year-old Hassam then committed himself to a healthier life style, including swimming.

His urban subjects began to diminish and he confessed that he was tiring of city life, as bustling subways, elevated trains, and motor buses supplanted the graciousness of the horse-drawn scenes which he so enjoyed capturing in earlier times.

"[44] In 1904 and 1908, he traveled to Oregon and was stimulated by new subjects and diverse views, frequently working out-of-doors with friend, lawyer and amateur painter Colonel C. E. S. Wood.

He produced over 100 paintings, pastels, and watercolors of the High Desert, the rugged coast, the Cascades, scenes of Portland, and even nudes in idealized landscapes (a series of bathers comparable to those of Symbolist Pierre Puvis de Chavannes).

"[48] In the midst of the vibrant city, Hassam painted July Fourteenth[49], Rue Daunou during the Bastille Day celebrations, a forerunner of his famous Flag series (see below).

[52] Hassam displayed six paintings at the landmark Armory Show of 1913, where Impressionism was finally viewed as mainstream and nearly an historical style, and displaced by the clamor over the radical revolution of Cubism, fresh from Europe.

Hassam viewed the new art trends from abroad with alarm, stating "this is the age of quacks, and quackery, and New York City is their objective point.

[56] Being an avid Francophile, of English ancestry, and strongly anti-Germany, Hassam enthusiastically backed the Allied cause and the protection of French culture.

[55] Although he had great hopes that the entire series would sell as a war memorial set (for $100,000), the pictures were sold individually instead after several group exhibitions, the last at the Corcoran Gallery in 1922.

[62] Hassam makes a patriotic statement without overt reference to parades, soldiers, or war, apart from one picture showing a flag exclaiming "Buy Liberty Bonds".

[63] In 1920, he received the Gold Medal of Honor for lifetime achievement from the Pennsylvania Academy of the Fine Arts and numerous other awards through the 1920s.