Abstract Although the non-profit literature has grown substantially, the issue of how revenue diversification affects non-profits has not been fully explored. This paper presents several disciplinary perspectives regarding the financing of non-profits, what determines their ability to diversify, and the consequent effects on their behaviour. It first develops an index for measuring revenue diversification and applies it to a national sample of charitable non-profits. The results indicate that, while the perception that most non-profits rely on a single revenue source is exaggerated, the institutions in our sample have somewhat concentrated revenue. Our findings also suggest that the activity of a non-profit and the proportion of its expenditures that it devotes to fund-raising affect its ability to diversify its revenues concentration. While a number of anomalies exist, the weight of our evidence suggests that diversified revenue sources are more likely to be associated with a strong financial position than are concentrated revenue sources. Researchers interested in studying the life-cycle of non-profits, the factors that give rise to stability and growth, and the constraints on non-profit behaviour would do well to consider the diversification index presented in this paper.