In 1969, in Stanley v. Georgia, the Supreme Court of the United States stressed that there is a constitutional right to form one’s thoughts and not simply to express them. The resources for thought shielded by jurisprudence on this right —books, films, and, more recently, video games—are cultural. How, scholars have recently asked, should it apply to means of changing minds that are chemical or mechanical? The concept of “cognitive liberty” was proposed 25 years ago to answer this challenge. Building on this effort, this chapter explores how chemical and mechanical transformations of thought raise distinctive questions for both “negative” and “positive” variants of cognitive liberty: our rights against others’ interference in our minds and to change them ourselves.