Practitioner involvement in evaluation, research, development, and other forms of disciplined inquiry that are small scale, local, grounded, and carried out by professionals who directly deliver those services is embraced across a wide range of professions as essential to good professional practice. However, little is known about the character, homogeneity or diversity, outcomes, motives, and practice of this activity. This article explores practitioner evaluation in social work, with an eye toward plausible connections with professional work across the public sector. The authors first explore the experience of doing practitioner evaluation, including its solitary or collaborative character, insider and outsider ascriptions and achievements, reflective moments regarding competence and capacity, and occasional glimmers of fascination with the work. The authors then explore contextualizing practitioner evaluation within its practice, agency, and professional cultures. Their third focus is through the lens of shifting practice and evaluation borderlines. The authors conclude with some provisional discussion of the implications for good practitioner evaluation. (Contains 2 notes and 3 tables.)