This chapter describes international maize-breeding research at the International Maize and Wheat Improvement Center (CIMMYT) across its first fifty years. Initially, breeders used landraces to create varieties whose seed, freely distributed through an international testing network, could be saved by farmers. A second phase in which CIMMYT forged partnerships with local and regional seed companies reflected the shift toward “market-led development.” This moderated free access to seed and fostered a gradual switch to hybrid technology. A trend among donors towards increased accountability and shorter funding cycles concurrently restricted CIMMYT’s investment in long-run research goals and accelerated a change of focus to Africa. Nonetheless, the development of germplasm tolerating drought and low soil fertility continued for decades, with eventual payoffs. Meanwhile, a long-running program to improve protein nutrition through high lysine maize varieties stalled due to lack of demand. In the twenty-first century, partnerships with global private seed companies allowed access to new technologies such as advanced screening methods, genomic selection, doubled haploids and gene editing.