We design a field experiment to test two theories of fund-raising for threshold public goods: Andreoni predicts that publicly announced “seed money” will increase charitable donations, whereas Bagnoli and Lipman predict a similar increase for a refund policy. Experimentally manipulating a solicitation of 3,000 households for a university capital campaign produced data confirming both predictions. Increasing seed money from 10 percent to 67 percent of the campaign goal produced a nearly sixfold increase in contributions, with significant effects on both participation rates and average gift size. Imposing a refund increased contributions by a more modest 20 percent, with significant effects on average gift size.