In recognition of the need to create new treatment approaches that will be appealing to and effective for emerging adults with serious mental health conditions, researchers have begun to create and evaluate programs and interventions that are specifically tailored to reflect the preferences and needs of the population. The literature that describes these new approaches—including both descriptions of interventions and guidelines based on expert consensus—expresses a high degree of agreement regarding practice principles that should guide intervention. However, beyond naming these principles, the literature provides little information about what the principles mean, or how principle-adherent practice can be recognized. This article describes a qualitative investigation of providers’ understanding of principle-driven practice in the context of programs and interventions for emerging adults with serious mental health conditions. The goal was to learn about how providers conceptualize the principles that drive their practice, and how they describe principle-adherent practice.