By examining musical theatre icons and their major collaborations starting from Oklahoma! (1943) and ending with Waitress (2016), this chapter chronicles the evolution of the American musical, as practitioners assembled creative teams in response to shifting economics and the rise of mediated popular culture on television and the internet. Film studios and corporations such as Disney now develop and produce their own musicals, bringing new resources and structures that both support and expand the collaborative creation of musical theatre. At the same time, regional theatres and not-for-profit venues developed new models of their own for participating in musical theatre collaboration. Whether conceived in consultation with a corporate producer or tested through a low-budget laboratory process, what's inside twenty-first-century American musicals remains the product of creative, collaborative relationships.