This article describes Dyadic Concordance Types(DCTs) to classify cases into Male-Only, Female-Only, and Both aggressed categories, and a reference category of Neither. Evidence from 32 nations is summarized on the percent of couples in each DCT. It indicates that across all nations, sample types, and gender of respondent, and regardless of whether the aggression was physical, psychological, or sexual, aggression in a family dyadic relationship was most often by both members of the dyad. When there was a sole perpetrator, although there was more variation in the percent in each DCT, the results tended to show a similar percent of Male-Only and Female-Only perpetration. Studies cited show that DCTs provide information that is beyond that obtained by analyses of the individual-level variables used to identify the DCTs. This reflects the family systems theory principle that the whole is greater than the sum of the parts. Statistically, it is analogous to the additional variance explained by use of interaction terms in a causal model. The Discussion suggests that identifying DCTs can enhance research, theories, and services for victims and offenders. These enhancements can be achieved if identification of the DCTs of the cases becomes a default starting point for research and practice concerned with family aggression.