The purpose of this paper is to analyze the role of interpreters during the negotiation of land surrender treaties signed with Canada's First Nations form 1850 to 1923. Firstly the context of the negotiations is examined and some preliminary information about the interpreters is provided. The role of interpreters includes the functions of 'negotiator', 'informant' and advisor', going beyond simple linguistic mediation. Secondly, some theoretical considerations are presented to conceive of interpreting as an instrument of assimilation and resistance, as well as a vehicle for transmitting values and not just content. By acknowledging and analysing the power of the interpreter to become 'visible' and intervene deliberately in the exchange, interpreting can be defined as a social, cultural and ideological act.