This chapter explores the concept of misinformation where it is discussed (primarily) as if it were a theoretical problem to be solved. Misinformation in this discursive form often manifests as conspiracy theories, and alternative explanations for (often) anomalous events. A number of examples of this discourse of misinformation are set out. A range of key literatures (particularly from competing sub-fields within psychology, from the sciences more broadly, as well as from communications and philosophy) that discursively frame misinformation (and contingent terms) in this way, are explored, using the toolkit introduced in the previous chapter. The conceptual bounds of this discourse are explored. Just as some examples of misinformation contain theories, so too are there competing theories about the nature of misinformation. Three dominant theories of misinformation across the literature are explored in detail, as a manifestation of pollution, as a virus (and meme), and as a type of marketplace. This chapter concludes with an exploration of the merits and limitations in each of these ways of conceiving of misinformation.