Using data from 720 publicly traded companies, this paper looks at the impact of the 2017 Tax Cut and Jobs Act through two different studies. Firstly, the paper finds that, on average, there was a reduction in the GAAP effective tax rate (ETR) of 8.88%. However, the first study identifies key firm characteristics that determine the actual observed change in ETR for any given firm. The biggest determinant of the change in ETR is a firm’s prior ETR, with percentage foreign income, R&D expense, and firm size as other significant predictors. The second study seeks to identify whether the tax change had any impact on firms’ investment behavior, one of the noted reasons for the policy change. The results did not show that the TCJA, reduction in ETR, had any impact on firm investment behavior as measured by capital expenditures and R&D spending.