Laeti^{[pronunciation?]}, the plural form of laetus^{[pronunciation?]}, was a term used in the late Roman Empire to denote communities of barbari ("barbarians", literally "babblers" - of outlandish tongues - i.e. foreigners, people from outside the Empire) permitted to, and granted land to, settle on imperial territory on condition that they provide recruits for the Roman military. The term laetus is of uncertain origin, but most likely derives from a Germanic word meaning "serf" or "half-free colonist". Other authorities suggest the term was of Latin, Celtic or even Iranian origin.

Laeti may have been groups of migrants drawn from the tribes that lived beyond the Empire's borders. These had been in constant contact and intermittent warfare with the Empire since its northern borders were stabilized in the reign of Augustus in the early 1st century. In the West, these tribes were primarily Germans, living beyond the Rhine. There is no mention in the sources of laeti in the Eastern section of the Empire. Literary sources mention laeti only from the late 3rd and 4th centuries.