Impulsivity is defined as acting prematurely without forethought or foresight. Three assessments of impulsivity were compared in companion dogs: the delayed reward task, cylinder detour task, and the Dog Impulsivity Assessment Scale (DIAS). A strong correlation was observed between the behaviour tasks, but neither behaviour task correlated with the DIAS suggesting that they are measuring different facets of impulsivity. Lack of early socialization also appeared to negatively affect dogs’ ability to be trained on the behaviour tasks. A study was then conducted to compare high (n=17) and low (n=14) socialized dogs’ performance on the cylinder detour task and DIAS. Low socialized dogs performed poorer (p < 0.05) on the cylinder detour task and had higher DIAS scores (p < 0.05) than high socialized dogs. Models of the cylinder detour task and DIAS also indicated that social factors in the first 12 weeks of life appear to significantly influence impulsivity. These results suggest that socialization influences the development of impulsivity in dogs which may guide owner behaviour during puppyhood.