Climate change is expected to cause a poleward shift of many temperate species, however, a mechanistic understanding of how temperature and species' life histories interact to produce observed adult range is often lacking. The authors evaluated the hypothesis that juvenile thermal tolerance determines northern range in gray snapper (Lutjanus griseus), a species commonly caught as juveniles along the US Atlantic coast well north of their adult distribution, using a combined laboratory, field and modeling approach. To evaluate the relationship between juvenile thermal tolerance criteria and adult distributions, the authors used the REEF database to quantify adult distribution. There was a strong correspondence between observations of adult gray snapper from the database of recreational divers vs. latitude with that of the predicted survival of juveniles vs. latitude from their modeling analysis. The agreement between the laboratory-derived thermal tolerance metrics, the spatial distribution of winter temperature, and the distribution of adult gray snapper support the hypothesis that the adult range of gray snapper is largely limited by the overwinter survival of juveniles.