A step-wise description of a self-report instrument to measure interpersonal conflict between marital partners illustrates the primary aspects of the development of a psychometric tool. Definition of the construct to be measured, formulation and classification of items, and appropriate methods to establish validity and reliability are discussed. Indications are considered for alternate forms of a scale, which include repeated measurement over time for the purpose of identifying patterns in human behavior in interaction within the family system. The procedure for constructing alternate forms of equal reliability is outlined.