Evolutionary theory predicts that grandparental investment should support the childbearing of adult children, but evidence from contemporary developed countries is mixed or relatively weak. One possible reason for this lack of clarity is that grandparental support for fertility may vary by country, the economic situation of the adult child's household, and the lineage and the sex of the grandparent. Objective We investigate the associations between grandparental investments and the intentions of mothers to have a second or third child in four European countries -- Bulgaria, France, Lithuania, and Norway -- while paying special attention to effect of the country, the financial security of the household, and the different grandparent types. Methods Using the first wave data (2004-08) of the Generations and Gender Surveys, we measured grandparental investment by the amount of child care help and emotional support mothers reported receiving from their parents. We studied these factors with binary logistic regression analysis. Results Both emotional support and child care help from grandparents were associated with increased fertility intentions in France and Norway. Emotional support was also associated with increased fertility intentions in Bulgaria, while grandparental child care help was associated with decreased intentions in Lithuania. Emotional support was more strongly associated with fertility intentions in financially secure households. Emotional support received from a maternal grandmother, a maternal grandfather, and a paternal grandmother; and child care help received from a maternal grandfather; were associated with an increased probability that a mother would report the intention to have another child. Conclusions Grandparental investment, especially emotional support, appears to be most influential in wealthier European countries and among more financially secure families. When a family's socioeconomic situation and the broader environment are generally favourable for having several children, grandparents may provide the "extra push" that supports the intention to have another child. (author abstract)