This chapter provides an overview of the design of the psychometric study. First, sampling issues are addressed, including who should be recruited and in what numbers, with guidance on anticipating the impact of planned statistical analyses. The relative merits of “clinical” and “non-clinical” samples are discussed, and the chapter reflects on “real world” gaps between methodological ideals (i.e., probability samples) and the accessibility of populations of interest for social service and health care providers. The development of a complete data collection package, including its components, layout, and sequence is outlined. Incorporation of relevant demographic indicators and the inclusion of standardized and non-standardized measures for examining evidence of construct and criterion-based validity are discussed. Well-designed scales and tests must be validated in thoughtfully constructed studies where recruitment and training of associates, anticipation of labor and costs, and plans for data management and entry have all been carefully considered.