Chapter 6 applies the relevance-based account of referring expressions to the phenomenon of null subjects in non-pro-drop languages. So-called diary-style nulls, it is argued, are ultimately driven by the interaction of effects and effort and therefore by the speaker’s aim of achieving optimal relevance. Three broad categories of null subject use in English are identified: an informal null subject where the omission leads to extra cognitive effects, a pressurized null subject where the speaker’s abilities are the crucial factor, and finally, an ostensively vague null subject, which is driven by the speaker’s preferences. These three categories are not presented as an exhaustive taxonomy of English null subjects, or as theoretically distinct. Rather they emerge as a result of a speaker aiming at optimal relevance in different discourse contexts, and they represent occasions where different elements in the overall equation of optimal relevance drive lexical omissions.