Studies focusing on genetic and social influences on maternal adjustment will illumine mother's marriage, parenting, and the development of psychopathology in her children. Recent behavioral genetic research suggests mechanisms by which genetic and social influences determine psychological development and adjustment. First, heritable, personal attributes may influence individuals' relationships with their family members. These genetically influenced family patterns may amplify the effects of adverse, heritable personal attributes on adjustment. Second, influences unique to siblings may be the most important environmental determinants of adjustment. We derive three hypotheses on maternal adjustment from integrating these findings from genetic studies with other contemporary research on maternal adjustment. First, mother's marriage mediates the influence of her heritable, personal attributes on her adjustment. Second, mother's recall of how she was parented is partially genetically influenced, and both her relationships with her spouse and her child mediate the impact of these genetically influenced representations on her current adjustment. Third, characteristics of mother's spouse are important influences on difference between her adjustment and that of her sister's These sibling-specific influences are unrelated to mother's heritable attributes. The current article develops this model, and the companion article describes the Twin Mom Study that was designed to test it as well, as its first findings. Data from this study can illumine the role of family process in the expression of genetic influence and lead to specific family interventions designed to offset adverse genetic influences.