Though some producer organizations have enabled developing country farmers to exploit new opportunities and/or cope with emerging challenges through developing and/or taking advantage of innovative mechanisms and institutions, there are many farmers who lack sustainable access to inputs and services as well as to remunerative output markets. This paper is intended to generate a better understanding of the conditions which make producer organizations capable vehicles by which farmers, especially small-scale farmers in developing countries, can reach markets in a dynamic and demanding trading environment, and respond to the needs of their clients and members. It aims at identifying lessons on the forms of organizations as well as the innovative mechanisms and institutions that producer organizations can adopt and/or help promote in response to challenges in the changing agricultural marketing systems, in particular, to strengthen the bargaining position of farmers