Abstract: Humanity’s survival depends on crops--the thin green line standing between us and calamity. To meet ever expanding human needs crops must become increasingly more productive, mainly through genetic gains which exploit diverse plant genetic resources (PGR), the raw materials for crop breeding. Through millennia, PGR have been conserved by, among others, farmers, gardeners, land managers, breeders, researchers, plant explorers, information technologists, and curators.  These stewards of our agricultural future have been nearly as diverse as the PGR that they have conserved. Their invaluable roles in underpinning the security of global agriculture have largely been underappreciated.  Furthermore, the challenges and complexity of successful PGR stewardship have been inadequately recognized. This presentation pays tribute to these stewards’ characteristic attributes and their past and present contributions to PGR conservation and sustainable use.  It describes the pervasive impacts of PGR on crop agriculture and explains how organizational structures, cultural milieus, conceptual models, international agreements, and technological developments affect PGR stewardship capacities. PGR stewardship involves many different components which are typically conducted over extended timeframes. Sustained, adequate support for PGR maintenance, a key component, has been the exception rather than the rule. Past and present PGR stewardship successes and challenges furnish numerous lessons for meeting future demands during an era of rapidly changing environmental, cultural, and technological factors, and when leadership is shifting to the next generation of PGR stewards. Such lessons include recognizing the importance to PGR stewardship of: dedicated and diverse PGR stewards, continual and persistent financial support for PGR genebanks and their staffs, protecting crop wild relatives, and safeguarding genebank collections from extreme weather and introduced pests and pathogens. In the future, PGR stewardship might be conducted more frequently and more adequately by multi-institutional networks enabled by advances in information technology and artificial intelligence.