Despite substantial rates of parent to child aggression (PCA) and intimate partner aggression (IPA) co-occurrence within families, the co-occurrence of PCA and IPA within incidents of aggression has not previously been examined. To do so, we developed the Children, Intimate Relationships, and Conflictual Life Events (CIRCLE) interview to simultaneously measure incidents of psychological and physical PCA and IPA. The CIRCLE interview was administered quarterly for approximately 1 year to 109 women and 94 men from 111 couples with a first born child approximately 32 months of age at study initiation. Demonstrating the CIRCLE interview’s ability to yield new knowledge about the nature of family aggression, we describe the frequency of aggressive incidents, the average number of aggressive behaviors within incidents, the daily occurrence of multiple aggressive incidents, and rates of within-incident PCA and IPA co-occurrence. With the exception of men’s physical IPA, aggression scores derived from the CIRCLE interview exhibited a relatively high degree of interpartner reporting concordance, as well as structural validity and convergent validity with common aggression measures. Aggression reports via repeated testing were not influenced by social desirability or attempts to avoid aggression. Participants who perceived enhanced memory for aggression as a function of study participation reported increasing PCA and IPA frequencies over time. In the prediction of child conduct and emotional problems, the CIRCLE interview demonstrated predictive validity and incremental validity over traditional aggression measures. For the first time, within-incident co-occurrence of PCA and IPA was documented and shown to uniquely impact child outcomes. Impact Statement Public Significance Statement-To help integrate the fields of intimate partner aggression and parent to child aggression research, we developed an interview to assess the occurrence and severity of incidents of each form of aggression. In this study we demonstrate that the interview is reliable and valid in a variety of ways and, for the first time, we document that aggression toward partners and children can occur within the same aggressive incident, with unique negative implications for children’s functioning.