This paper describes and compares code-switching (CS) by lay participants and institutional representatives in data involving English-speaking migrants collected in legal and healthcare settings in Northern Italy. In both settings CS by foreign end-users is found to be relatively common in sequentially ‘reactive’ positions; with the exception of nonce borrowings, lay participants take the initiative in CS more rarely, mainly when pressing personal concerns are at issue. CS by institutional representatives shows a functional sensitivity both to broad institutional aims and to the specific sub-aims of the various phases of the encounter; its greater prevalence in the healthcare setting can, it is argued, be traced to the need to create a collaborative relationship in order to successfully diagnose and treat the patient. Implications of the results for theories of mediated interaction and for the training of community interpreters are discussed.