Stress assignment is one of the most widely-known and controversial aspects of present-day Mapudungun (aka Araucanian) phonology. Here, the diachrony of the phenomenon is explored based on the available written record spanning 1606–1936. Having surveyed these sparse but suggestive data, and contrasted them with present-day evidence, we suggest four distinct stages of development. Ultimately, we go on to argue that Mapudungun has undergone changes both to the morphological and metrical domains which determine stress assignment. At the level of the morphology, stress appears to have changed from marking the edge of verbal roots, to marking the edge of stems. In terms of metrical units, the apparent lack of weight-sensitivity in the earliest stages of the language is replaced by a decidedly weight-sensitive system towards the end. Finally, it is argued that stress assignment in Mapudungun is subordinate to morpho-phonological transparency both synchronically and diachronically, allowing the position of stress to vary in order to highlight the morphology."