Rosenthal provides a critical history and analysis of the connections between mainstream and experimental theatre in New York, from the 1960s to 2020, with a focus on Broadway. She argues that Broadway and mainstream theatre underwent multiple and significant transformations during the 1960s and in the decades that followed. Rosenthal analyzes the work of playwrights, directors, composers, choreographers, and designers who made art both downtown in experimental theatres and uptown on Broadway. The concept of the “mainstream experimental” is used as a descriptor for Broadway throughout the following half century, as commercial theatre continued to push and shape US society and culture at large. Alongside artists, pathbreaking producers off and on Broadway are the focus of this chapter, along with the prominence of ensemble-based musicals and dramatic works and the success of solo performances on Broadway. The contributions and legacies of LGBTQ artists such as Tony Kushner, Larry Kramer, and Lisa Kron, and Black artists including August Wilson, George C. Wolfe, Ntozake Shange, Anna Deavere Smith, and Jeremy O. Harris, are central to Rosenthal’s argument and critique.