Transcranial direct current stimulation (tDCS) was used to investigate whether anodal stimulation of the left or right dorso-lateral pre-frontal cortex (DLPFC) compared to a sham group modulated performance on a number of judgment and thinking tasks: 1. vignettes measuring heuristic thinking, 2. logic syllogisms, and 3. the cognitive reflection test (CRT). Results from fifty-four participants showed that anodal tDCS to the right DLPFC was associated with an increase in cognitive reflection performance (correct answers to CRT and heuristic vignettes) as compared to left DLPFC and to sham. Logic thinking scores were reduced following anodal tDCS to the left DLPFC. A second experiment confirmed these results for the right DLPFC, and in addition showed that repeated (two sessions) stimulation also increased performance in the CRT. These findings are broadly consistent with an account of cognitive inhibition of prepotent responses in reflective thinking, that could not be explained by differences in impulsivity. Two further experiments investigated the role of dorsal and ventral areas in the Cambridge Gambling task, measuring quality of decision making (QDM), risk-taking (RT) and delay aversion (DA). tDCS real stimulation enhanced QDM and increased RT compared with sham, but no tDCS effects were found on DA.