American art came of age with the first important modern movement by a group of New York painters who became known as Abstract Expressionists. In the 1940s and 50s their aggressive action painting challenged the School of Paris. Tenaciously American (though several were born abroad), these painters were not content to imitate European masters and styles. They were struggling to express their own transcendental values that emphasized freedom, impulse, and instinct, and favored large-scale canvases with broad, improvisational brushwork. Harold Rosenberg, author of the phrase “action painting,” offers his valuable insights, as does fellow critic Clement Greenberg. Predictably, the two differ in their opinions, keeping alive the issues raised by the paintings themselves.