To be in circulation is to be in motion, to flow along or through some course or circuit. _Circulation_ may refer to any movement between people or places, but the term has special meanings for print media such as comic books. In the strictest sense, a periodical’s circulation refers to how many copies are sold on average; circulation thus has a relationship—albeit an inexact one—with audience. In its broadest sense, it opens onto a rich vein of theorizing about how culture shapes our experiences of space, time, and social connection. Since the rise of the penny press in the early to mid-nineteenth century, most periodical publishers have adopted a hybrid business model, selling both the newspaper or the magazine itself and advertising space inside. Ads subsidize lower cover prices, encouraging larger circulations, and everybody wins. In this arrangement, then, publishers serve two masters: the reader, who must be persuaded to buy a copy, and the advertiser, who must believe these readers are worth addressing. Both audience size and quality must be considered. Some publishers—the great general-interest magazines of the twentieth century such as _Look_ and _Life_, for example—seek to maximize their readership, pitching content to their conception of the broadest...