Despite the tendency of some academic disciplines to assume that the nuclear family is normative, the family takes a number of different forms cross-culturally. Regardless of family form, family members typically cooperate in raising children. Intergenerational help (from grandparents to parents and children), for example, is a cross-cultural universal. Such cooperation means that the availability of kin may be one salient factor in deciding whether and when to have children. Here I consider the evidence for whether the availability of kin does influence fertility, and whether these relationships vary cross-culturally. I find evidence from middle and lower income populations that the presence of kin does increase fertility, and that these relationships are plausibly driven by cooperation between family members. In higher income contexts, associations between kin and fertility are mixed, and appear particularly sensitive to how kin availability and support is measured. There is some evidence that certain measures of support from kin (such as emotional support or help with childcare) increases the likelihood of subsequent births, but kin support is not always positively associated with fertility. Family matters for fertility, then, though these relationships may be complex and context-specific. Policy needs to take this diversity into account, and should not focus exclusively on the nuclear family model, nor neglect the roles other family members play in reproductive decisions.