This article proposes an original theory of interdisciplinarity and a revisionist history of interactions between the sociology and history disciplines. It examines relations between historians and sociologists in Germany and France over the course of the twentieth century, focusing on several key moments of interdisciplinary activity.The present article differs from the existing literatures on historical sociology and interdisciplinarity in several ways. Most accounts of historical sociology since the 1980s have depicted an endeavor taking place entirely within sociology, occluding other axes of interdisciplinarity. Rather than focusing on sociologists working historically, or historians working sociologically, I begin by reconstructing both of the disciplinary fields within the metafield of academic disciplines. I then consider the full range of interactions and practices coming from both directions. According to most previous accounts, disciplines evolve as unified totalities, generations, or waves. I analyze disciplines as social fields-as dynamic, relational, and internally heterogeneous and divided assemblages. Rather than asking how entire disciplines interact with one another, I focus on the ways specific actors and groups within disciplines relate to specific parts of external disciplines. I try to map the entire array of interactions and repulsions between disciplines. Rather than simply describing interdisciplinary practices, I ask how these practices have been supported or hindered by causal forces located within disciplines and at varying distances Acknowledgements: I am grateful to Julia Hell, Phil Gorski, Howard Brick, participants in the symposium on "The Sociology of the Social Sciences 1945-2010" at the University of Copenhagen, 9-11 June 2011, and several anonymous CSSH reviewers for comments on earlier versions of this paper.