Despite increases in their application and improvements in their structure, there is a paucity of reliable and valid scales compared to the complex range of problems that social workers and other health professionals confront daily. They need to be able to design rapid assessment instruments (RAIs) to fit their specific situations, and with this step-by-step guide by RAI experts, that prospect will be much less intimidating. For each stage of RAI development, from conceptualization through design, data collection, and analysis, the authors identify critical concerns, ground them in the growing conceptual and empirical psychometric literature, and offer practical advice. A presentation of the basics of construct conceptualization and the search for evidence of validity is complemented by introductions to concept mapping and cross-cultural translation, as well as an in-depth discussion of cutting-edge topics like bias and invariance in item responses. In addition, they critique and illustrate factor analysis in exploratory and confirmatory strategies, offering guidance for anticipating elements of a complete data collection instrument, determining sampling frame and size, and interpreting resulting coefficients. This pocket guide provides a comprehensive start-to-finish overview of the basics of scale development, giving practical guidance that practitioners at all levels will be able to put to use.