BACKGROUND: Self-help interventions intended to help nonclinical individuals regulate their emotions can have important social benefits (i.e. mental disorder prevention, well-being promotion). However, their mean effect size on well-being is generally low, possibly because there are considerable between-individual differences in the response to these interventions. The present study examined whether individuals' baseline levels of emotional well-being and engagement in emotion regulation strategies moderate the effects on these same variables in a 4-week self-help cognitive-behavioral intervention intended for typical adults. METHODS: Data were collected from 158 nonclinical French adults (n = 95 for the control group, n = 63 for the cognitive-behavioral group) using experience sampling. Emotional well-being was assessed, as well as the engagement in three emotion regulation strategies (i.e. cognitive reappraisal, problem solving, and appreciation). RESULTS: As expected, the post-test scores on some variables were significantly predicted by the interactions between the intervention and the pre-test scores on these same variables. In particular, it was the participants with the most negative baseline levels (i.e. low emotional well-being, low engagement in appreciation) who benefitted most from the intervention. CONCLUSIONS: Results are discussed in the light of current knowledge on between-individual differences in how individuals respond to interventions.