Glyphosate is the world’s most used herbicide. There are currently 32 weedy species with resistant populations in 25 countries, although at present there are no reported cases of glyphosate resistance in the UK. As glyphosate use and selection pressure increases in the UK there is an excellent opportunity to investigate the potential for glyphosate resistance, and the evolutionary processes that may lead to resistance. The variability in standing genetic variation to herbicide susceptibility between weed populations can affect the amount of selection pressure and generations needed for resistance to evolve. If herbicide doses act within this standing genetic variation there may be a reduction in sensitivity due to a buildup of minor alleles related to reduced sensitivity. This thesis has investigated the glyphosate response of three UK weedy species, Alopecurus myosuroides (blackgrass), Anisantha sterilis (sterile brome), and Arabidopsis thaliana. Dose-response experiments showed significant variation in susceptibility between populations of all three species. Glasshouse selection experiments tested if glyphosate sensitivity could be further reduced under directional selection with below field rate doses, in Alopecurus myosuroides populations. Following selection, ten of eleven selected lines showed significantly different ED50 and ED90 values compared to unselected control lines, demonstrating that there is potential for selection of reduced glyphosate sensitivity, which may result in compromised field efficacy. Fitness cost experiments for two glyphosate-selected lines showed no major fitness costs associated with decreased glyphosate susceptibility both with and without wheat competition. Analysis of multi-parent advanced generation inter-cross Arabidopsis thaliana lines highlighted an area on chromosome 2 of the Arabidopsis thaliana genome that may be associated with variation in glyphosate susceptibility. These results are discussed in the context of the possibility of glyphosate resistance evolution in the UK.