The use of vague language is one of the most common features of everyday spoken English. Speakers regularly use vague expressions to project shared knowledge (e.g., pens, books, and that sort of thing) as well as to make approximations (e.g. around sevenish; he’s sort of tall). Research shows that many of the most common single word items in a core vocabulary form part of vague language fixed expressions (e.g. thing in that kind of thing). This chapter will address the use of vague language in a new corpus of academic English, the Limerick-Belfast Corpus of Academic Spoken English (LIBEL CASE). The LIBEL corpus consists of one million words of spoken data collected in two universities on the island of Ireland, one in the Republic of Ireland and one in Northern Ireland. Analysis of the LIBEL corpus identified forms and functions of vague language in an academic context and these findings are compared with two corpora of everyday spoken language from the Republic of Ireland and the United Kingdom, the Limerick Corpus of Irish English (LCIE) and the Cambridge and Nottingham Corpus of Discourse in English (CANCODE). Cross-corpora comparison allowed us to look at how forms and frequencies of certain vague language expressions vary across casual and formal/institutional contexts. Within the academic data, the paper builds on Walsh’s work (see for example Walsh 2002, 2006) to show how vague language use is relative to mode of discourse at any given stage of classroom interaction. It is suggested that these qualitative differences are a valuable means of understanding the complex relationship between language and learning.