This paper describes the procedures used to develop and validate the Nurse-Midwifery Clinical Data Set (NMCDS), a uniform, standardized tool for the purpose of data collection about midwifery clinical practice. The instrument was developed under the auspices of the ACNM Division of Research, and it was shown to be valid for the purposes of quality assessment data collection through the use of specific instrument development and field testing procedures. These procedures included consensus panel development, expert panel review, standardization, feasibility analysis, and validation through comparison with previous outcome data and record review. The 1990 version of the NMCDS is appended to the article.