This paper discusses the why and how of one Norwegian university department, which conducts all their teaching via English as a lingua franca. Why did they opt for English as official medium of instruction? Has the department's English-only policy lead to the sole use of English, or are Norwegian and other languages also employed in particular circumstances, irrespective of the policy? The paper links Fishman's domain theory to code-switching theory (as defined by Fishman, Auer and Heller).