Most couples in committed relationships have implicit or explicit rules regarding infidelity. However, not all partners view infidelity in the same way, and the discrepancy in opinions can lead to problems in the relationship and can complicate the healing process. The purpose of this study was to better understand how people define infidelity and the variables that influence perceptions about infidelity. A mutlimethod design was used to collect quantitative and qualitative data on participants\u27 perceptions and definitions of infidelity. Quantitative data was collected through participants\u27 answers to questions on a scale about perceptions of potentially unfaithful behaviors that was developed for the purpose of this study. The scale included physical, emotional, and cyber behaviors that could be perceived as unfaithful. Participants\u27 answers were compared to certain variables including age, gender, relationship status, sexual orientation, religiosity, parental marital status, sexual orientation, personal involvement in extradyadic relationships, and knowledge of parental involvement in any extramarital involvement in order to determine whether or not these variables predicted perceptions of infidelity. Qualitative data was collected through participants\u27 answers to open-ended questions about how they define infidelity. The results of the study showed that perceptions of infidelity are most influenced by gender, sexual orientation, how frequently individuals attend religious services, knowledge of an affair within the family of origin, level of education, and personal experience with infidelity. The analysis of the qualitative data resulted in a richer understanding of how infidelity is defined, including: boundary violations, a type of infidelity (physical, emotional, or cyber), lack of consent from the betrayed partner, and hurt. These results can enhance the understanding of researchers and clinicians about how people define infidelity, what behaviors are perceived as infidelity, and how certain variables influence these perceptions
