This paper presents the findings from a cross-national study of expert mental health social workers in Melbourne, Australia and San Jose, California, USA. In this study, expert social workers were selected based on a peer-nomination process and they were invited to participate in two-hour focus group interviews in which they described memorable practice situations. Detailed accounts of these practice situations were gathered from nineteen Australian and American expert practitioners employed in community-based mental health settings. The study findings corroborate many of the dimensions that are explicated in a theory of professional expertise developed by Fook et al. (2000). Further, the findings describe the skilful and ethical comportment of these social workers in the context of often complex and challenging practice situations. Narrative accounts are used to demonstrate the distinguishing dimensions and features of expert practice described by Fook and her colleagues, especially when providing services to people with chronic mental illness. In-depth articulation of practice expertise using cross-national data enhances social work research and pedagogy by providing important exemplars that inform more fully the development of empirically based practice theories.