We argue that behavioural public policies (BPP) should be categorized by the kind of mechanism through which they operate, not by the kind of treatment they implement. Reviewing the energy consumption BPP literature, we argue (i) that BPPs are currently categorized by treatment; (ii) that treatment-based categories are subject to mechanistic heterogeneity: there is substantial variation of mechanisms within each treatment type; and (iii) that they also display mechanistic overlap: there is substantial overlap between mechanisms across treatment types. Consequently, current categorizations of BPPs do not reveal the conditions of their efficacy and should be revised to better reflect mechanistic information.