"Comics, comic books, and graphic novels are increasingly the target of seriously scholarly attention in the humanities. Moreover, comic books are exceptionally complex documents, with intricate relationships between pictorial and textual elements and a wide variety of content types within a single comic book publication. The complexity of these documents, their combination of textual and pictorial elements, and the collaborative nature of their production shares much in common with other complex documents studied by humanists—illuminated manuscripts, artists’ books, illustrated poems like those of William Blake, letterpress productions like those of the Kelmscott Press, illustrated children’s books, and even Web pages and other born-digital media. Comic Book Markup Language, or CBML, is a TEI-based XML vocabulary for encoding and analyzing comic books, comics, graphic novels, and related documents. This article discusses the goals and motivations for developing CBML, reviews the various content types found in comic book publications, provides an overview and examples of the key features of the CBML XML vocabulary, explores some of the problems and challenges in the encoding and digital representation of comic books, and outlines plans for future work. The structural, textual, visual, and bibliographic complexity of comic books make them an excellent subject for the general study of complex documents, especially documents combining pictorial and textual elements."