Previous research on gender differences in behavior has led to seemingly contradictory findings about generosity. From data generated by 290 subject pairs, we find that women are more sensitive than men to the costs of generous actions when deciding whether to be generous. The factors that affect the level of generosity observed in our experiments are reciprocal motivation, the level of money payoffs, and the level of social distance in the experimental protocol. The relatively greater sensitivity of women to the costs of generous behavior can explain most of the apparent inconsistencies in previously reported findings. (JEL C70, C91, D63, D64)