#ryanandmath

what kind of background do you need to start learning about this? I'm trying to understand just from the wiki page and it seems like category theory, but I'm not sure what else

Yeah, category theory (at least up to the point where you can prove that limits in functor categories are computed pointwise and things about filtered colimits et cetera, possibly more than that idk I'd have to think about it) although idk I found it useful to have some grounding in a bunch of other branches so as to have some examples to fall back on when playing with the concepts. (i believe this is what is called "mathematical maturity", which is kind of a cop-out, I know.)

Again though, as a first introduction to topos theory, I would recommend Sheaves in Geometry and Logic: A First Introduction to Topos Theory by Mac Lane and Moerdijk.

Seriously. That's a much better first book to read in the subject.

(seriously)