This article presents the results of a literature review related to volunteerism in urban forestry in the United States. Themes explored were inductively emergent from the research reviewed and included 'volunteer demographics', 'motivations of volunteers', 'benefits of volunteering', 'volunteer engagement and barriers', 'value of volunteering', and 'volunteer recruitment and retention'. Urban forestry volunteers are often motivated by personal, social, and environmental considerations. Volunteers in urban forestry may not be representative of a cross-section of the communities that they are serving, rather they are often middle-aged, well-educated white women. Further research is required both to ascertain barriers to volunteerism and to enhance future volunteer recruitment and retainment efforts. Volunteers in the United States account for 5% of municipal tree care in urban forests - accounting for an estimated $35 million USD in value. Volunteers perform critical urban forestry-related tasks that aim to increase urban tree canopy cover through tree selection and planting efforts. Volunteers encourage urban tree survival by advocating for, as well as performing, important maintenance-related duties including the administration of supplemental watering and urban tree pruning. With proper training and support, volunteers may accurately perform important data collection efforts that may inform management decisions and urban tree care maintenance programmes.