This project considers the relationship between aggressive and assertive communication behaviors; two concepts rarely studied in tandem with one another. The goal of this project was to develop and assess the construct validity of the Aggressive Assertive Communication Instrument (AACI). In order to examine the content validity, internal consistency, and associations between the AACI and external variables, three studies were conducted. Study 1 was a pilot study designed to examine the theorized factor structure and item composition of the AACI. To assess the validity of the measure, the proposed items were correlated with individual difference variables commonly examined and associated with interpersonal conflict (i.e., agreeableness, extraversion, locus of control, and taking conflict personally). The aims of Study 2 were to further examine the factor structure and item composition of the AACI and to cross-validate the AACI with dispositional traits (i.e., agreeableness, entitlement, exploitativeness, extraversion, family communication patterns, self-esteem, and trait anger). In Study 3, convergent and divergent validity were assessed with existing aggressive and assertive measures (i.e., BAAI, BPAQ, VAS, and AI) and dispositional tendencies (i.e., conflict management style and argumentativeness). Additionally, three conditions were developed to assess how the AACI may change or differential relate to tested variables when individuals reflected on their behavior with an acquaintance, close friend, or romantic partner. Results from these studies revealed a consistent and stable four-factor structure comprised of two assertion-related factors (i.e., direct communication and relationship orientation) and two aggression-related factors (i.e., verbal aggression and physical aggression). A non-orthogonal rotation method (i.e., Promax rotation) method was utilized in the EFAs as the factors were expected to correlate. CFAs were utilized to further examine model fit. Results indicated utility in assessing aggression and assertion concurrently. The four factors and the final 23-item AACI had acceptable internal consistency reliability and related to concepts as expected. Although external variables often related to the two aggression-related or the two assertion-related factors in tandem, several dispositional traits were uniquely related to only one of the AACIs four factors. These results further justify the need for a multidimensional measure that assesses both aggression and assertion with multiple factors.