Fundraising is a form of investment for charities: they invest a certain amount on marketing each year and expect to generate a return in the form of donations. Data seems to show a positive association between fundraising spending and donations, but does this accurately reflect the causal returns on the fundraising efforts? I will present a structural model which characterises the revenue generation and decision making of charities, in addition to an empirical strategy which enables identification of the own charity returns, spillover effects and strategic effects between charities. I find (extremely) tentative evidence that the collective returns outweigh the individual returns amongst Green Charities in the UK, as fundraising by one charity encourages fundraising by other charities (strategic complementarity), and also generates higher returns for other charities (positive spillovers). I will also discuss the limitations of using the fundraising ROI as a measure of fundraising efficiency, the effect of competition in the charity sector and the implications of these findings for charity managers and regulators.