Social scientists have documented the influence of family statuses on volunteering, ignoring intrafamily effects. Using newly issued data from the Current Population Survey on the volunteer behavior of 19,626 American couples, we test two competing theories concerning spousal influences on volunteering. Substitution theory predicts that spouses will trade off volunteer work; complementarity theory predicts that spouses' volunteer work is positively linked. Using structural equation methods to control for simultaneity bias, we find support for the complementarity theory. The wife's influence, however, is stronger than the husband's. Spousal influence is stronger if both spouses volunteer in the same domain. The findings underline the importance of close relationships in mobilizing volunteer workers.