I propose an account of the supply domain for testimonial knowledge: intentional acts in which a speaker offers her word on a matter to her intended audience. Such acts are effected by speech acts of telling exploiting a shared language. From this account I derive an account of the proper doxastic response to such a telling that P, namely accepting the speaker’s offered word that P. I show that one who takes the speaker’s word is committed to holding that she was epistemically so placed as to properly offer her word – namely, that she knows that P. I use my account of the supply domain for and proper response to testimony, to show what is wrong with a thin reliabilist conception of the good supply domain for testimony. The thin conception has it that any reliable testifier is an apt source. I argue that only those who know what they state properly offer their word, and only from them can knowledge be gained through the Core Mechanism, taking the speaker’s word for what she states.