We present evidence from a field experiment in Lusaka, Zambia that male involvement in the decision to seek out family planning services leads to substantial reductions in utilization. This phenomenon appears to be driven by average differences by gender in the demand for children rather than by a general distrust of or lack of information about family planning technologies among men. Study participants were offered a voucher that granted access to an appointment with a family planning nurse without a wait in line. Demand for family planning services is high, as evidenced by the 41 percent overall rate at which these vouchers were redeemed. Women were randomly assigned to receive the voucher either by themselves in private, or together with their husbands. Takeup among women assigned to receive the vouchers with their husbands was 9 percentage points (18 percent) lower than among women randomly assigned to receive the vouchers alone. We find evidence that this reduction in takeup was larger if husbands wanted more children than their wives, and stronger evidence that this reduction was larger among young couples than among older couples with completed fertility. There is no evidence that assignment to couples treatment reduces voucher use for women whose husbands want no more children, and evidence for a 12 percentage point reduction in use in the subsample of women whose husbands do want more children. Taken together, these results suggest that the unitary and collective bargaining models do not sufficiently richly describe the bargaining process over fertility within the household. Furthermore, policies or technologies that shift relative control of contraceptive methods from men to women may significantly increase contraceptive use and reduce average fertility in some contexts.