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This paper is motivated by a desire to understand and quantify the extent to which millennials are truly different in their activity-travel behavior when compared with Generation X that preceded them. In order to conduct the inter-generational comparison and control for a number of confounding factors in determining the “millennial difference”, data from the 2001 and 2017 National Household Travel Survey (NHTS) are utilized. Subsamples of Generation X and millennials are drawn respectively from these data sets; both subsamples were constrained to be 26-30 years of age in the respective periods to control for age effects. The analysis involved estimating a simultaneous equations model system of car ownership, frequency of internet use, frequency of shared mobility services use, and driver vehicle miles of travel (VMT). The model system accounted for a number of effects including socio-economic/demographic effects, period effects (reflecting changing economic and technological conditions), geographic effects, and cohort (millennial) effects. In computing the sizes of various effects in explaining differences in driver VMT between the two cohorts, it is found that the socio-economic/demographic effect size is the largest. All other effect sizes are very small; the millennial effect, although statistically significant, is tiny in comparison to the socio-economic/demographic effect size. The isolation of the millennial effect size is, however, not straightforward because the other effects may themselves be influenced by the cohort effect. Nevertheless, the millennial effect appears very small, at least when comparing millennials in the 26-30 years range with …