Despite the relevance of language use in expert testimony, researchers have rarely scrutinized the linguistic and interactional processes of constructing an expert identity. This study, rather than reifying the concept of expert and leaving it as an unproblematic legal argument, examines how this institutional identity emerges in and through discursive interaction between the prosecuting attorney and a physician (who is also the defendant) in trial cross-examination. Using Goffman's notion of footing, the article examines how both prosecutor and defendant mobilize direct and indirect quotes, repetitive parallelism, epistemic modality, counterfactuals, evidentiality, sequencing, and specialized tokens of the medical register to contextualize shifting into and departing from an expert identity. I would like to thank the Office of Social Science Research at the University of Illinois at Chicago for financial help. Don Lance (as always) and Richard Cameron provided detailed comments and guidance throughout the course of writing. Thanks are due to Wayne Kerstetter, Mike Maltz, Pat McAnany, Joe Peterson, and Sarah Ullman for comments at an early presentation. Finally, I deeply appreciate the very detailed comments of Elizabeth Mertz and W. M. O'Barr, which I have tried to incorporate as much as possible.