Introduction From the Green Revolution that took place around the mid-twentieth century until today, the agricultural sector has undergone substantial changes on account of rapid developments in the agricultural sciences, especially those due to plant genetics. These changes have signifi cantly aff ected plant genetic diversity, which is composed of two main types: one is inter-specifi c or species diversity that refers to the number of diff erent species (i.e., crops) that are present in the fi elds; the other is intra-specifi c diversity and it refers to the variation in the genetic composition of a particular species (forms and types). This chapter reviews key developments that have had an impact in crop diversity at large, because those developments often have consequences for both the number of crops and their own genetic make up. For example, most of the technological advances in plant genetics serve to enhance intra-specifi c diversity (i.e., better adapted cultivars); however, the adoption of improved cultivars may foster the demotion of non-improved crops, thus aff ecting the number of crops planted in the fi eld. This chapter tackles developments related to crop improvement, and the social implications of changes in the ownership of genetic resources. Finally, the chapter presents initiatives for conserving and using genetic diversity, thereby off setting the negative impacts of modern developments. It presents a selected number of issues of social debate around modern agriculture and genetic diversity, ending with an outlook to agriculture in the near future.