We study the influence of perceived descriptive social norms on subsequent giving behavior to nonprofits, explore how social information can influence these norms, and provide insight for fundraising practice. A survey conducted in a nonprofit organization first shows that donors use their beliefs about the descriptive social norm to inform their own donation behavior. Donors who believe that others make high contributions tend to make high contributions themselves. Next, a laboratory experiment demonstrates the influence of social information on the descriptive social norm and consequently on giving. These results suggest strategies for fundraising practice. Informing donors of contributions made by another person influences their perceptions about the descriptive social norm, which in turn influences their giving behavior. We conclude with a discussion of theoretical and practical implications.