In "Threshold Concepts and Troublesome Knowledge," Jan Meyer and Ray Land (2006) explain that "interviews and wider discussions with practitioners in a range of disciplines and institutions" (6) led them to identify the characteristics associated with threshold concepts that have become familiar to researchers who have adopted or adapted this framework for thinking about learning and teaching. That is, threshold concepts are transformative, probably irreversible, integrative, potentially troublesome, and bounded. It's this latter idea that is significant for this chapter. Specifically, as Meyer and Land explain, threshold concepts are "possibly often (though not necessarily always) bounded in that any conceptual space will have terminal frontiers, bordering with thresholds into new conceptual areas. It might be that such boundedness in certain instances serves to constitute the demarcation between disciplinary areas, to define academic territories" (6). They follow this with two illustrations: one from a faculty member in cultural studies and one from veterinary sciences, both of whom explain the consequences for students of seeing through or seeing with threshold concepts from other disciplines, or of invoking ways of thinking and practicing (Hounsell and Anderson 2009) associated with operationalization of threshold concepts inconsistent with the threshold concepts of the discipline. The idea that threshold concepts serve as portals into disciplinary participation has become an important one for teachers, learners, and researchers working with the idea.