Our understanding of what exactly needs protected against in order to safeguard a plausible construal of our ‘freedom of thought’ is changing. And this is because the recent influx of cognitive offloading and outsourcing—and the fast-evolving technologies that enable this—generate radical new possibilities for freedom-of-thought violating thought manipulation. This paper does three main things. First, I briefly overview how recent thinking in the philosophy of mind and cognitive science recognises—contrary to traditional Cartesian ‘internalist’ assumptions—ways in which our cognitive faculties, and (...) even our beliefs, can be materially realised by as well as stored non-biologically and extracranially. Second, and taking brain-computer interface technologies (BCIs) and the associated possibility of ‘extended’ beliefs as a reference point, I propose and defend a sufficient condition on freedom-of-thought violating (extended) thought manipulation. On the view proposed, the right not to have one’s thoughts or opinions manipulated is violated if one is (i) caused to acquire non-autonomous propositional attitudes (acquisition manipulation) or (ii) caused to have otherwise autonomous propositional attitudes non-autonomously eradicated (eradication manipulation). The implications of this view are then illustrated through four thought experiments, which map on to four distinct ways—what I call Type 1-Type 4 manipulation—in which, and with reference to the view defended, one’s freedom of thought is plausibly violated. (shrink)