We focus on the distinction between sufficient and necessary conditions of systematic and heuristic processing. This distinction is addressed in the context of a specific domain of research: the influence of mood states on processing strategies. We first review empirical research into the interplay of affect and cognition, drawing on examples from persuasion and person perception. The research indicates that being in a happy mood fosters heuristic processing, whereas being in a sad mood fosters systematic processing. Next we address how these findings have been used to infer decreased processing motivation or decreased processing capacity in the context of dual-processing models. Specifically, we focus on empirical and conceptual inconsistencies that raise doubts about the assumption that increased heuristic processing reflects decreased motivation or resources. Finally, we suggest an alternative account–namely, that affective influences on the use of heuristic strategies may be independent of processing motivation or capacity–and present some relevant data, before we address general theoretical and methodological implications for dual-process models. (PsycINFO Database Record (c) 2007 APA, all rights reserved) (from the chapter)