Dispersal biology at an invasion front differs from that of populations within the range core, because novel evolutionary and ecological processes come into play in the nonequilibrium conditions at expanding range edges. In a world where species' range limits are changing rapidly, we need to understand how individuals disperse at an invasion front. We analyzed an extensive dataset from radio-tracking invasive cane toads (Rhinella marina) over the first 8 y since they arrived at a site in tropical Australia. Movement patterns of toads in the invasion vanguard differed from those of individuals in the same area postcolonization. Our model discriminated encamped versus dispersive phases within each toad's movements and demonstrated that pioneer toads spent longer periods in dispersive mode and displayed longer, more directed movements while they were in dispersive mode. These analyses predict that overall displacement per year is more than twice as far for toads at the invasion front compared with those tracked a few years later at the same site. Studies on established populations (or even those a few years postestablishment) thus may massively underestimate dispersal rates at the leading edge of an expanding population. This, in turn, will cause us to underpredict the rates at which invasive organisms move into new territory and at which native taxa can expand into newly available habitat under climate change.hierarchical Bayes | shift | spatial sorting | relocation data | hidden states M any populations are shifting their range edges in response to climate change (1, 2) and other anthropogenic stressors (3, 4), and invasive species are spreading rapidly worldwide (5, 6). We need to predict rates of range shift to manage these changes, but (despite sophisticated theory on the processes underlying range shift), models routinely underestimate the rate of spread (7) because they underestimate the frequency of longdistance dispersal. Not only are rare long-distance dispersal events difficult to document (8, 9), but populations in the spreading vanguard are subject to powerful ecological and evolutionary forces not experienced by conspecifics within the range core. On the expanding range edge, individuals mate assortatively by dispersal ability ("spatial sorting") (10, 11); deleterious mutations can surf to fixation (12, 13), and parasites and pathogens may get left behind (14, 15). These differences could all affect dispersal rates and mean that to predict rates of range shift, we need to actually measure dispersal at the invasion front.Understanding the differences in dispersal rates at and behind an invasion front also may clarify the roles of plasticity, evolution, and ecology. For example, covariation of dispersal rates with conspecific or pathogen density implies a role for plasticity (e.g., density-dependent dispersal) or ecology (the effect of parasites and pathogens) rather than evolutionary processes in driving dispersal-rate variation. In contrast, higher dispersal rates at the invasion front versus further ...