Sequential mixed methods is a useful research design to inform second-stage methodology when investigating an area of practice in which relatively little is known. This article describes how focus group findings were used to measure advance care planning practice among community-based case managers. The initial qualitative study utilized focus groups to explore aspects of practice in this area. Data revealed themes that embodied ambiguous views of advance care planning, divergent roles in practice, a continuum of practice activities, and multiple facilitators and barriers to practice. In order to further examine case managers' advance care planning practices, qualitative findings were used to develop the Case Managers Advance Care Planning Practices Instrument. Implications for qualitative to quantitative measurement are discussed.