(Measuring) Readability: a critical look at sustainability reports through standard formulae and NLP AbstractThis study characterises and problematises the language of corporate sustainability reporting along region, industry, genre and content lines by applying readability formulae and Natural Language Processing (NLP) to a manually assembled 2.75-million word corpus. Readability formulae reveal that, despite its wider readership, sustainability reporting is still a very difficult to read genre, one sometimes more difficult than financial reporting. Although we find no industry impact on readability, region does prove an important variable, with Australian reports significantly more complex than others. These results not only highlight the impact of legistative contexts but also language variety itself as an underexplored variable. Finally, the study lays bare some of the weaknesses of default readability formulae, which are unable to detect American reports' more active language or lower lexical density in UK/EU reports, and demonstrates the merits of NLP in report readability analysis as well as the need for more accessible sustainability reporting.