Much conventional wisdom about programs written by volunteers is wrong. Book review of The Comingled Code: Open Source and Economic Development. By Josh Lerner and Mark Schankerman. MIT Press. Its main contribution consists of two surveys - one of users of software, the other of developers - that are unprecedented in both scale and scope. More than 2,300 companies and nearly 2,000 programmers, spread across 15 countries, both rich and poor, filled out questionnaires. And Messrs Lerner and Schankerman asked a lot of questions, from how much open-source software a firm has implemented to whether governments should mandate the use of such programs. The findings contradict much conventional wisdom. Many open-source developers work for firms that develop both open-source and proprietary programs and combine them in all kinds of business models. More than a quarter of companies happily mix and match both sorts, in particular in poorer countries. Yet the finding that open-source advocates will like least is that free programs are not always cheaper. The authors argue that governments should make sure that the two forms of software compete on a level playing field and can comingle efficiently. One way of doing this would be to promote open standards to ensure that proprietary incumbents do not abuse a dominant position.