The genetic diversity found in populations of crop wild relatives is an essential resource for future crop breeding, but populations are at risk of loss before germplasm has been fully conserved in genebanks. This chapter describes best practice for targeting and identifying species, and review knowledge about the variation in wild plant populations to guide the timing of collecting and approaches for genetic sampling. Indicators are presented for seed quality, ripeness and dispersal. Techniques for collection of seed, herbarium vouchers and associated data are reviewed with examples drawn from the Adapting Agriculture to Climate Change (Crop Wild Relative) project. Further research is needed to find optimal approaches for handling of seed to ensure high longevity of seed collections, and improved tools are needed to guide sampling of genetic diversity of crop wild relatives.