Haugen's model (in "Sociolinguistics," Penguin, Harmondsworth, pp 97-111, 1972 [1966]) of standardisation has been widely adopted in general histories of particular languages, not least because of its clarity and simplicity. In this article, I focus on its treatment of codification, with a view to suggesting refinements to this part of the model. In particular, I discuss the relationship between codification and prescription on the one hand, and between prescriptivism and purism on the other. Haugen makes no distinction between codification and prescription either in the original version of his model (Haugen 1972 [1966]), or in its revised version (Haugen in "Blessings of Babel. Bilingualism and language planning problems and pleasures," Mouton de Gruyter, Berlin, 1987). Indeed, he seems to consider codification and prescription as broadly interchangeable, suggesting that the typical products of codification are a prescriptive orthography, grammar and dictionary. Whilst Milroy and Milroy ("Authority in language: Investigating language prescription and standardisation," 2 edn, Routledge, London/New York, 1991) do differentiate codification and prescription, neither model mentions purism, although Deumert and Vandenbussche ("Germanic standardisations: Past to present," John Benjamins, Amsterdam/Philadelphia, 2003) argue that it is essential to consider its role in the history of standardisation. I offer definitions of the different terms and argue that, when considering the role of prescriptivism and purism in linguistic standardisation, it is important to distinguish between the author's/work's intention, use of metalanguage, and effect. Finally, I adapt George Thomas's model for assessing purism to the assessment of prescriptivism, thereby avoiding viewing prescription and description as a simple dichotomy.