Compelling arguments from researchers studying the rhetoric of science have convinced both scientists and humanists that technical writing involves invention, or discovery of the available means of argument. If we agree that inventio is crucial to technical writing, however, we encounter a problem: namely, that the rhetor engaged in invention as part of a technical writing process does not necessarily have expertise in the subject matter of the composition. What, then, is the expertise that the technical writer contributes to the invention process? Working from the notion that knowledge is an activity rather than a commodity [1], I argue that a technical writer's expertise in invention lies in an ability to adapt rhetorical heuristics to situations of interdisciplinary collaboration. This focus expands our understanding of how invention works when the goal of communication is producing knowledge across disciplinary boundaries, rather than winning an argument with persuasive techniques.1