This essay examines the role of adaptation in Guillén de Castro’s play El curioso impertinente . Castro’s play, in spite—or perhaps because—of its relationship to Cervantes’s novela of the same name, has received relatively little attention as a work of its own merit, and particularly for its representation of early modern ideas on adaptation. The majority of the critical work about Castro’s play has focused on a single issue: fidelity to the source text. Moving beyond questions of textual fidelity, the essay shows how Castro’s version of El curioso impertinente stages adaptation within the play itself and how that staging offers insight into Castro’s own adaptive practices. The essay argues that Castro reworks Cervantes’s novela by exploring adaptation as a creative process of appropriation and intervention, both for the play as a whole and as part of the dramatic action of the piece.