It is generally agreed that the Catholic Church played a highly significant role in almost every dimension of the life of Irish migrants in nineteenth-century Britain. This chapter traces the impact of the Irish on the Catholic population of Manchester and its internal dynamics, the reactions of local Protestants, the gradual build-up of church institutions and its shifting concerns. It discusses the extent to which the church remained Irish in outlook and preoccupations. The chapter examines how from the earliest times there were concerns amongst the clergy about the external dangers threatening the faithful. These took the form of Protestant prejudice, often stirred up by local preachers, and Protestant proselytism through the allocation of Catholic orphans and foundlings to non-Catholic homes. The Salford Diocese Catholic Protection and Rescue Society was one of the most notable guardians of the boundaries of faith and morals.