How do you organize your books?

Nora Krug in The Washington Post:

My bookshelves are a mess. It’s not just that I have too many books and too little space. I’m also simply disorganized. It wasn’t always so. Shelves I put together years ago, pre-children, remain generally intact: a full bookcase of poetry, alphabetized by author, and several jam-packed bookcases of fiction, also by authors’ last names. These shelves now serve primarily as decoration or reference or as a lending library for guests. But there’s more, much more: the tumbling pile on my desk — propping up the computer I am typing on — and the volumes stuffed frantically in the bookcase in my bedroom and stacked in towers on and around my nightstand. These are the books that are part of my daily life — for work, for pleasure, sometimes both. There is no rhyme or reason to how I arrange them, but as I read in one of the books I consulted (then discarded) to help deal with my little problem: “If it’s where you meant it to be, then it’s organized.” I am adopting that as my book-organizing principle. Don’t tell my kids.

More here.