The merger of Dow and DuPont, the acquisition of Syngenta by Chem- China, and the acquisition of Monsanto by Bayer have recently reshaped the global seed and biotech industry and caused concern about growing mar- ket concentration. This review documents market concentration in seed and agricultural biotech markets and discusses its causes and impacts. The avail- able evidence suggests that concentration in seed markets varies strongly by crop and by country, while markets for biotech traits are considerably more concentrated.