There is a clean image of knowledge transmission between thinkers that involves sincere and reliable speakers, and hearers who carefully assess the epistemic credentials of the testimony that they hear. There is, however, a murkier side to testimonial exchange where deception and lies hold sway. Such mendacity leads to sceptical worries and to discussion of epistemic vice. Here, though, I explore cases where deceit and lies are involved in knowledge transmission. This may sound surprising or even incoherent since lying usually (...) involves saying something that is false. Even if a liar unwittingly tells the truth, those believing their testimony would not acquire knowledge. In §1, however, I suggest a range of examples where lies can be used to transmit knowledge. The kinds of cases upon which I focus are those involving ‘engineered knowledge’, where a speaker skilfully manipulates another into having a true belief. Such cases are epistemologically significant for several reasons. First, they are counter-examples to a range of widely held assumptions about knowledge. We have, for example, cases where sincerity is not necessary for knowledge transmission, where there is knowledge from falsehood, and, as we shall discuss in §2, knowledge that is fragile or not safe. Second, in §3 and §4 I suggest that engineered knowledge is best captured by a virtue theoretic approach to testimonial transmission. (shrink)