Due to labour shortages in key areas, early-modern Spain frequently employed foreigners to provide missionary and military manpower, administrative personnel, and technical expertise. Like their Flemish, English, and French contemporaries, Irish Catholics served Spain as priests, soldiers, bureaucrats, and operatives. The Irish colleges functioned as elements of these service networks, although this aspect of their activity remains relatively obscure. In part, this is because the colleges and their students are usually viewed in the context either of Spain’s international Catholic commitments and its geopolitical strategy or from the vantage of the Irish mission. Yet service to Spain and to the Spanish monarchy was also an important function of the collegial network and one that was not at odds with but rather complementary to its better known mission to the Irish church. Spanish support of the colleges, in fact, appears to have been at least tacitly predicated on Irish readiness to serve in the diverse religious missions of the Habsburg and Bourbon monarchies. Over time, this arrangement adapted to Spain’s changing needs and to the exigencies of the Irish mission. By the end of the eighteenth century, however, this largely complementary arrangement began to come under strain as Irish bishops sought more control over the formation and placement of clerical students trained overseas.