The rapidly growing field of positive psychology has introduced a number of measures that can be used to quantify and enhance human flourishing. Surprisingly little is known, however, about which of those measures is most malleable. A systematic literature review was conducted to begin addressing this gap. The aim of this review was to rank the most widely-used measures in positive psychology, in descending order, from most malleable to least. To do so, the review method was to collect all interventional studies which attempted to change participants’ scores for each measure, then calculate a mean effect size for each measure. The results of this search found that such studies have only been conducted on 5 of the 24 VIA Strengths, showing an incomplete picture of measure malleability and creating a clear call to action for further research to explore the malleability of character strengths and other positive psychology measures.