Depends on the type of e-book. If it's a kindle book, you can cite a location number.

Great question. I have tons of epub books and haven't found a satisfactory answer. I cite by chapter and paragraph number, which is very cumbersome.

I avoid ebooks if possible, but when I do use them I try to cross reference with the search function on Google Books to get an actual page number, then treat the reference as if it came from the hard copy. That's probably too complicated, I know.

/u/jschooltiger, I think this should have a meta tag.