A nonprofit “governance quality index” was developed to enable verification and falsification of contemporary theoretical insights on social service organizations. Indicators were generated based on an extensive qualitative exploration. For the quantitative validation, a data set was composed of 526 respondents from 52 organizations. Five subdimensions of governance quality are introduced and are recommended to be used as separate scales, rather than combined into a single score on governance quality. Furthermore, the recommendation is made to rely on multiple raters per organization to assess governance quality or related concepts, given the substantial within-organization variance found.