Using a longitudinal, prospective adoption design, the authors of this study examined the effects of the environment (adoptive parents' depressive symptoms and responsiveness) and genetic liability of maternal depression (inferred by birth mothers' major depressive disorder [MDD]) on the development of fussiness in adopted children between 9 and 18 months old. The sample included 281 families linked through adoption, with each family including 4 individuals (i.e., adopted child, birth mother, adoptive father and mother). Results showed that adoptive mothers' depressive symptoms when their child was 9 months old were positively associated with child fussiness at 18 months. A significant interaction between birth mothers' MDD and adoptive mothers' responsiveness indicated that children of birth mothers with MDD showed higher levels of fussiness at 18 months when adoptive mothers had been less responsive to the children at 9 months. However, in the context of high levels of adoptive mothers' responsiveness, children of birth mothers with MDD did not show elevated fussiness at 18 months. Findings are discussed in terms of gene-environment interactions in the intergenerational risk transmission of depression. (Contains 2 tables and 1 figure.)