People tend to contribute to a charity only when they are asked to. Although this so-called 'power of asking' is a well-known technique among fundraisers, the existing literature does not pay much attention to the role of donation requests in charitable giving. We estimate the causal effects of charitable solicitations on both the propensity to give and the amount of charitable contributions using a unique data set, which was designed to measure the giving behavior in the United States. In order to address the endogeneity of the donation requests due to non-random solicitation of charitable donors, we link this data set to IRS data on charitable organizations and the 2000 Census and propose identifying instruments. After controlling for the endogeneity, we find that people are both more likely to contribute to a charity and also donate more when they are asked to. This effect is robust under different specifications and with different sets of instruments and is much larger compared with the estimates of univariate models. Furthermore, we argue that some identifiable characteristics of individuals are associated with the higher probability of being solicited. In particular, we find some evidence that income, age, education, and race play significant roles in explaining the selection of potential charitable donors.