This thesis investigates the invisibilisation of Austrian German features in 18th_and early 19th-century texts. The term invisibilisation refers to a process of implicit or explicit stigmatisation, which prevents the use of certain varieties and variants in writing (cf. Langer & Havinga 2015). Since written sources are the only source available to historical linguists any features not used in writing remain literally invisible to researchers. In this thesis, the role of language ideologies, 18th-century grammarians, and Empress Maria Theresa's school reform (1774) in the invisibilisation of a number of Austrian German variants is examined. In the period under investigation (1744--1834), the majority of these variants were replaced by their East Central German (ECG) equivalents, which were prescribed by 18th -century grammarians, in formal writing. The thesis offers a comparison between top-down language policy and language use, as evidenced in three divergent text types. A quantitative and qualitative study of reading primers, issues of the Wienerisches DiariumlWiener Zeitung, and handwritten petitionary letters revealed that the e-apocope in feminine and plural nouns and Upper German variants of the verb to be in the 1st and 3rd person plural present active indicative (wirlsie seynd) disappeared from these formal text types in the second half of the 18th century. The dative -e was, in comparison, implemented later and less consistently, particularly in the Wienerisches Diariuml Wiener Zeitung and in the petitions. The absence of the prefix ge- in past participles, on the other hand, was clearly avoided by the mid-18th century, while the development of the ending -t in regular past participles was not completed by 1834. The differences in the development of these features indicate that there was not one single factor that led to the invisibilisation of Austrian German variants. It was rather the interplay of Empress Maria Theresa's appeal for a language reform, the normative work of 18th -century grammarians, the implementation of educational reforms, and the early introduction of ECG variants in newspaper issues that resulted in the disappearance of these variants from formal writing.