Because the different languages spoken by the first nations of British Columbia were extremely difficult, most Catholic missionaries preached and taught in the Chinook jargon, a trade language. However, all natives did not know the jargon, so they often had to use interpreters as well. This article shows some of the problems the missionaries had with interpreters, especially in the 19th century. Moreover, the linguistic activities of a few missionaries serve to illustrate what was done during the mission era as far as translation, writing, lexicography and invention of alphabets go.