Since Miyake and his colleagues (2000) published their seminal paper on the use of confirmatory factor analysis (CFA) to parse executive function (EF), CFA methods have become ubiquitous in EF research. In their interesting and thoughtful Focus article, "Executive Function: Formative Versus Reflective Measurement," Willoughby and colleagues evaluate the application of these methods to date and raise several fundamental questions about the match between typical applications of CFA and the construct of EF. They make the provocative suggestion that approach to CFA typically used (i.e., reflective measurement) may not capture the "true" nature of the EF construct, and they propose that EF is better captured using formative or causal indicators. EF is a notoriously difficult construct to define, and the findings of Miyake and colleagues (2000) seemed to bring coherence to the field by providing an overarching model of EF, parsing it into components that fit together within a hierarchical structure. Should the present paper motivate EF researchers to reject this model in favor of a formative measurement approach? It is important to note that the empirical findings presented in the Focus article are equivocal, with approximately half of the studies reviewed supporting each of the 2 approaches based on the vanishing tetrad calculations. Consequently, this paper represents a starting point for discussion and further research rather than a conclusion. Willoughby et al. state that, in their view, "few researchers have thought deeply about" the question of how individual EF tasks relate to latent EF. The hope is that this Focus article and set of commentaries start a conversation that helps to remedy this problem and motivates continued efforts to improve measurement of EF across development.