 Levels of organization have traditionally provided the framework for the debate on downward causation, where the question is whether higher-level entities or properties can exert causal influence on lower-level ones (e.g., Bechtel 2008; Campbell 1974; Emmeche et al. 1997, 2000; Kim 1992, 1999; Craver &amp; Bechtel 2007). The idea of downward causation is closely connected to emergentism, and is often seen as one of its core tenets (Emmeche et al. 1997, 2000; Kim 1999). Examples of putative downward causation include psychological states causing physical behavior, the activity of an organism causing changes in the tissues and cells of that organism, and cell-level processes such as synaptic communication causing molecular changes. Downward causation seems prima facie to be common or even ubiquitous in experiments and explanations in the life sciences (Craver &amp; Bechtel 2007; Love 2012). However, in contemporary philosophy, downward causation is often approached with skepticism. If it is understood as higher-level things or properties exerting some kind of physically measurable influence on lower-level things, there seems to be no evidence for it (McLaughlin 1992). Downward causation also faces metaphysical difficulties, most importantly the much-debated causal exclusion argument (e.g., Kim 1992, 1999, 2005). To put it very roughly, the core of this argument is that if we accept the plausible assumption that all physical occurrences must have sufficient physical causes, it is not clear how there could be room for additional higher-level causes of lower-level physical effects. For more on causal exclusion and downward causation, see the entries  mental causation  and  emergent properties.