William E. Cross Jr. (born 1940) is a theorist and researcher in the field of ethnic identity development, specifically Black identity development. He is best known for his nigrescence model, first detailed in a 1971 publication, and his book, Shades of Black, published in 1991. Cross's nigrescence model expanded upon the work of Black psychologists who came before him, and created an important foundation for racial/ethnic identity psychology. It has proved a framework for both individual and collective social change. Throughout his career, Cross has been concerned with racial/ethnic identity theory and the negative effects of Western thought and science on the psychology of Black Americans, specifically the need for “psychological liberation under conditions of oppression.”