© 2020, Springer Nature Limited. We undertook a systematic review to identify and summarise studies on hardcore smoking and hardening to: determine the degree of variability in definitions of hardcore smoking and hardening; assess the evidence for claims that smokers are becoming increasingly hardened within the context of harm reduction as a policy initiative; and identify the determining characteristics of a hardcore smoker. We searched five electronic databases from 1970 to mid-April 2018 using the search term “smok* AND hard* AND (tobacco OR cigar* OR nicotin*)”. We included studies if they included a definition of hardcore smokers and/or hardening, and provided a prevalence rate for hard core smokers or empirical evidence for hardening. Definitions of hardcore smoker varied substantially across studies. Hardening was not evident in the general smoking population and we found mounting evidence of softening occurring in smoking populations. These results indicate that hardening of smokers is not occurring and that calls for policy interventions on this basis should be challenged.