Looking back at the end of my academic career, it looks like mental energy is still a hot topic in today’s research and practice in occupational health psychology, as it was a couple of decades ago. This applies particularly to burnout (low mental energy), but also  to work engagement (high mental energy), which was introduced more recently. In this insider view, I am taking stock and try to answer four questions: (1) How well can we assess mental energy? (2) What is the prevalence of mental energy in the Netherlands? (3) What do we know about the antecedents and consequences of mental energy? (4) To what extent are interventions to increase mental energy evidence based? The paper is concluded with a discussion about the relationship between science and practice, in which five examples are presented of important issues for practice, which, so far, have not been adequately covered by scientific research; i.e., short measurement tools, benchmarks, organizational interventions, severe burnout, cost-benefit analyses (download full article – in Dutch).