Factors affecting the growth of larval, juvenile, and adult northern quahogs, Mercenaria mercenaria, are reviewed. Larval growth is affected by temperature, salinity, current speed, dissolved oxygen concentration, and the amount of suspended sediments in the water, along with such nutritional factors as food quantity and quality. Growth of post-set juvenile and adult quahogs is similarly affected by the same physical and nutritional factors. Recent work suggests that there is a strong genetic contribution to quahog growth rate and that selective breeding programs may be useful for producing rapid growth strains. A growing body of evidence suggests that larval growth rates are poor predictors of post-set juvenile growth rates. Indeed, preliminary evidence suggests that shorter larval development periods correspond with higher rates of growth in post-set animals. Further research into this aspect of the developmental biology of quahogs is recommended.