<p>The genetic diversity found in plants is a vital asset for present and future human populations. Useful genetic diversity for food production is primarily located in crop wild relatives (wild plant taxa that can donate adaptive traits to crops) and crop landraces (traditional crop varieties maintained by farmers). Both groups have crucial roles in crop diversification and varietal improvement. In this Review, we examine the geographic partitioning of taxonomic and genomic diversity, current threats, and the range of potential in situ and ex situ conservation techniques available to sustain diversity. Other values and perspectives on the conservation of plant genetic resources (typically associated with the biocultural and socio-ecological value of landraces) should be considered when planning and implementing conservation strategies, but they are beyond the scope of this Review. In situ and ex situ conservation applications require improved integration to ensure complementary conservation and that in-situ-conserved resources are as easily available to end users as they are from ex situ gene banks. Action on plant genetic resource conservation, policy and infrastructure at the global, regional and national levels is essential to preserve and use crop wild relative and landrace diversity.</p>