Despite the substantial growth of research interest on interdisciplinary collaboration and intellectual exchange, relatively little attention has focused on interdisciplinarity in the context of the academic journal system. In this paper, we ask a series of questions about peer-reviewed, academic journals which aim to span disciplinary boundaries. Data on a total of 789 journals established in 2008 were culled from Ulrich’s Periodicals and classified into discipline-based and interdisciplinary journals based on their mission statements. Principal findings: Roughly 25 percent of peer-reviewed journals established in 2008 claimed interdisciplinarity as part of their mission; Interdisciplinarity varies substantially by primary subject classification, from less than 10 percent in mathematics and physics to a majority of journals in public health and communications; Despite the prominence of biology and biomedical fields in discussions of interdisciplinarity, few of the new journals in these fields are interdisciplinary in focus. Paradoxically, many interdisciplinary journals are highly specialized; that is, while they span more than one field or one approach (basic research, clinical applications), their span of inquiry needs to be understood as focused on a highly delimited topic area. A typology of six types of interdisciplinary journals emerges from the data. While some high-status interdisciplinary journals, eg Science and Nature, are tremendously valuable in facilitating cross-disciplinary communication, the proliferation of comprehensive interdisciplinary journals would most likely hinder rather than facilitate scholarly communication.