The use of consumer health informatics (CHI) interventions is proliferating rapidly with little consensus about how CHI interventions should be designed or implemented. While CHI interventions have been shown to improve clinical outcomes, barriers to their use remain. This chapter describes a well-developed conceptual model for program evaluation and suggests how it can be used to guide the design and implementation of CHI interventions, with the goal of supporting the intended outcomes of these interventions and minimizing the unintended outcomes. The chapter then provides an overview of how knowledge from three human factors domains can inform the CHI interventions design and implementation components of the evaluation model. By integrating human factors principles and methods into the evaluation model, developers can reduce barriers to use and minimize resulting unintended consequences of CHI interventions.