He published "Modern Negro Art" in 1943, the first comprehensive study in the United States of African-American art. Porter decisively placed African-American artists within the framework of American art. He was the first to recognize and document the significant contributions these artists made to the history of American art. With Porter's systematic approach, "Modern Negro Art" became and still is the foundation of African-American art history and for later texts. Porter's interest in nearly forgotten and often ignored artists of African descent was sparked by reading a brief article on African-American landscape artist Robert Scott Duncanson. Due to the account's brevity, Porter followed his curiosity to research Duncanson and other artists of African descent.