jats:titleAbstract</jats:title>jats:pCatherine of Siena (1347‐1380) is well known as a saint and mystic with a colourful biography. Recent scholarship has begun to recognise Catherine's substantial political contributions. She wrote letters to notable political figures including Bernabò Visconti and Pope Gregory XI, and also brought her influence to bear in person, visiting numerous Tuscan cities as well as Avignon and Rome. There has been little investigation, however, into the relationship between Catherine's writings and major political discourses of the period. This article offers evidence that Catherine should be viewed within the jats:italicbonum commune</jats:italic> tradition of high medieval political thought. Like other Dominican political thinkers of the period, Catherine was particularly interested in the concept of jats:italiccaritas</jats:italic>, which she used to justify her involvement in political disputes such as the War of the Eight Saints (1375–8) between the papacy and Florence, and the disputed papal elections of 1378. Recognising that the content of Catherine's writings was political as well as spiritual provides an important counterpoint to accounts of late fourteenth‐century Italian political thought which give excessive prominence to 'secularising' humanists. This study also challenges lingering assumptions that the political thought of the early Renaissance must be studied through a narrow (and male) canon.</jats:p>