Using a collection of medals held at the Denver Museum of Nature & Science, Tarnished Promises presents an updated overview of the history and story of peace medals through an examination of their legacy in the modern world. Accompanying the history and analysis are images of thirteen exemplar peace medals from the DMNS collections and their accompanying object biographies. Peace medals paradoxically worked as tools of colonialism but also Native American agency, sovereignty, power, resistance, and change in response to growing challenges. Their widespread adoption by Native people in North America both prefigured and coincided with the many ways in which Native Americans and First Nations peoples worked to adapt to the unwelcome and undesirable changes wrought by expanding western colonialism. The unique individual histories behind the medals and the larger peace medal story suggest how material objects can hold several, sometimes contradictory, meanings and be influenced by varied strands of culture and historical memory. Tarnished Promises tells this complex story in two parts, with the first detailing the history of Indian peace medals from 1670 to the present day and the second part exploring their meaning at different points in time and to different peoples. The first book-length treatment of peace medals using an anticolonialist perspective, Tarnished Promises is significant to scholars and the general public interested in numismatics, American history, Indigenous studies, and museum collections.