Public service and bilateral interpreting are, in broad terms, two of the oldest interpreting modalities. From ancient times, public authorities in frontier areas used bilingual cultural mediators to communicate with their subjects. Besides the many well-documented examples of diplomatic interpreters in Renaissance courts and in the Arab kingdoms of northern Africa, documents in medieval Spain and in colonial America reveal numerous translation- and interpreting-related activities. Records from the 13th to the 17th centuries back up this linguistic mediation exercise in several areas of public life. They also show a trend towards the definition of the interpreters’ professional profiles: legislation applicable in Spain and in America regulated practical aspects of admission to the trade, remuneration, workplace, and code of conduct, well before the establishment of professional associations or guilds. On both sides of the Atlantic, including northern and southern America, the regulation of the profession was particularly detailed in the fields of justice administration and the exchange or liberation of captives. These areas do not entirely coincide with specific settings of public service interpreting today. However, the authors think that those rules and regulations from the past are valuable references for a profession that the Western societies seem to have rediscovered in the last two decades, in the context of vast migration phenomena.