Threats to the validity of inferences and conclusions regarding the effects of applied interventions have been a major dilemma for social scientists and evaluators for several decades. One mechanism for reducing threats to internal validity and improving warrants for cause-and-effect conclusions in nonrandomized investigations and evaluations is the inclusion of nonequivalent dependent variables as an element of structural design. In this chapter, the rationale for, history of, and examples from practice for using nonequivalent dependent variables to reduce internal validity threats, as well as some warrants supporting their increased use, are described. © Wiley Periodicals, Inc., and the American Evaluation Association