Six weed species are confirmed glyphosate resistant in Australia: annual ryegrass (Lolium rigidum), awnless barnyard grass (Echinochloa colona), windmill grass (Chloris truncata), liverseed grass (Urochloa panicoides), great brome grass (Bromus diandrus) and flaxleaf fleabane (Conyza bonariensis). The number of glyphosate-resistant populations of these weeds has increased dramatically in recent years, particularly for annual ryegrass (347 populations), barnyard grass (58), flaxleaf fleabane (49) and windmill grass (10). The majority of these infest cropping paddocks and adjacent non-agricultural land, such as roadsides, in the summer cropping region of Australia. The latest research on their ecology, levels of glyphosate resistance and mechanisms of glyphosate resistance are reviewed, with a focus on awnless barnyard grass and flaxleaf fleabane as case studies. This new information is being used to develop best weed management strategies for these resistant biotypes. Another threat is that glyphosate-resistant biotypes may also develop resistance to other herbicides, if the glyphosate alternatives are used repeatedly without stopping seed-set on the sprayed survivors. The risk for these six species to develop resistance to Group A herbicides, such as haloxyfop and quizalfop, Group I phenoxy herbicides, such as 2,4-D for flaxleaf fleabane, and Group L herbicides, such as paraquat, is explored. These risks need to also be taken into account when devising best weed management strategies for glyphosate-resistant biotypes.