The most effective charities are hundreds of times more effective than typical charities, yet few donors prioritize effectiveness. Why is that? How might we increase the effectiveness of charitable giving? We review the motivational and epistemic causes of (in)effective giving. Many donors view charitable giving as a matter of personal preference, which favors decisions based on emotional appeal rather than effectiveness. In addition, while many donors are motivated to give effectively, they often have misconceptions and cognitive biases that reduce effective giving. Nearly all research on charitable giving interventions focuses on increasing donation amounts. However, to increase societal benefit, donation effectiveness is likely to be more important. This underscores the need for research on strategies to encourage effective giving. Effective altruism is a philosophy and social movement that advocates using the most effective, evidence-based strategies to benefit others. Here we focus on charitable giving, a domain in which ordinary people can have a large impact.Most behavioral research on charitable giving focuses on donation amounts, but the impact of giving depends more on the effectiveness of the charities people support than on how much they give. We review recent research on the factors that promote (in)effective giving.There are motivational and epistemic obstacles to effective giving: People are often drawn to less effective charities, and to the extent that people want to give effectively, they typically do not know how to do it.We discuss strategies to encourage effective giving. Several strategies are feasible and warrant further research, as the potential social benefits are large.