What functions does “collaboration” play in our moral and political practices and how did it come to play those roles? We use the term “collaboration” to identify a valued partnership, but it also names a morally compromised association and functions as a reason for blaming and punishing complicitous behavior. However, it has also played nefarious political roles: shoring up patriarchy, legitimizing ethnic cleansing, and bolstering a myth of national unity. “Collaboration” plays various roles because it is both ambiguous and vague. It is ambiguous in that there are multiple conceptions of collaboration, and it is vague because it contains borderline cases that are difficult, even impossible, to resolve. An exploration of “collaboration” combined with the history of its coming of age shows why its study is so vexing and how it functions in unexpected and disturbing ways.