A study of the notes readers leave behind — in library books, in the endpapers of borrowed novels, in the margins of photocopied handouts nobody meant to keep.

Each piece in this volume is written separately, by a different contributor, and stands on its own — but read together they start to argue for the same thing: that the sidebar, the footnote, the underline in someone else's pen, has always been where the real thinking happens.

New entries are added to this volume as they're written. There's no fixed number planned.