Parent resistance to vaccines represents another clinical context where physician authority has eroded while patient agency has strengthened. This is largely a sociological perspective, but it has critical public health consequences. Drawing on a corpus of video recorded well-baby clinic visits, we examined 22 cases where parents resisted routine childhood vaccinations. Extending prior research on treatment resistance, we identify three bases for this resistance: fear, adverse experiences, and ideology. We show that when parents indicate that their resistance is rooted in fear or adverse experiences, it is inherently easier for physicians to build a tailored persuasive response to parents whereas with ideology-based resistance, it is much more difficult. We suggest that when physicians can identify fears and adverse experiences that underlie ideology-based resistance, this will provide a route for persuasive work. Additionally, this chapter demonstrates the utility of a language-based approach in the realm of medical sociology.