If, as the end of Chapter 2 suggested, a right to perceive with technology is often better understood as stemming from our freedom of thought than of freedom of speech—what doctrines can mark the limits of such a right? How can they avoid the problem that led the Court, in Zemel v. Rusk, to emphasize that we don’t have an unconstrained right to seek knowledge anywhere it is to be found? This chapter explores a number of possible answers to this question—drawing principally from First Amendment doctrines that bar government action when it is (1) motivated by an interest in suppressing speech, (2) attacks speech equivalents, or social practices that have First Amendment value. There can, this chapter argues, be equivalents for these in a doctrine of freedom of thought and perception. But it is also necessary to move beyond these familiar First Amendment models and explore new doctrine for newly defined rights.