Abstract Expressionism was a post-World War II art movement that began in New York in the 1940s and 1950s. Artists used non-traditional techniques like action painting to express themselves freely without a specific subject. Two main concepts were energetic gestures using impulsive brushwork and large fields of color. Major artists included Jackson Pollock, known for his drip technique paintings, Mark Rothko who created emotional color field paintings, Willem de Kooning who painted abstracted figures and landscapes, and Lee Krasner, Pollock's wife. The movement marked a shift to American modern art and freedom of expression.