This paper aims at positioning producer cooperatives within the Transaction Cost Economics theory, one of the most cited and prolific theories on management studies. To accomplish this goal, I will answer the questions what is a cooperative, which transactions producer cooperatives regulate, under which market conditions they operate, and where are the boundaries for such organizations. This paper offers a comprehensive framework to study producer cooperatives, adopting a comparative institutional point of view, where producer cooperatives are compared with markets, firms and other hybrid types.