Underutilized plant species are generally defined by their unexploited economic potential, making them an appropriate focus for market development. This paper analyses the role of collective action in the process of market development for minor millets, an underutilized plant species, in the Kolli Hills of Tamil Nadu, India. Based on a series of focus group discussions, we analyze the role and involvement of self-help groups in the minor millet marketing chain recently set up by the M.S. Swaminathan Research Foundation. We then compare the role of collective action in this new market with the cases of marketing chains for cassava and organic pineapples, two cash crops with expanding production in the same area. Our analysis shows the critical role of collective action as a necessary but not sufficient condition for the successful commercialization of underutilized plant species for the benefit of the poor and the conservation of agro-biodiversity.