There is growing interest in the health-promoting potential of human-companion animal relationships from a broad public health perspective while acknowledging barriers to ownership, particularly for older adults. Companion animal fostering is an alternative to pet ownership that aligns with the Ottawa Charter health promotion principle that caring for others in everyday settings promotes health. This narrative review of the literature on companion animal fostering draws on Te Whare Tapa Whā (the four-sided house), an indigenous model of health that is influential in Aotearoa/New Zealand, and the Ottawa Charter. We found that companion animal fostering can be considered health-promoting for human and non-human animals, using a broad and multidimensional understanding of health. As well as improving the long-term outcomes for homeless animals, companion animal fostering has the potential to promote the health of the individuals, families, and communities who provide foster homes. Our review highlights the importance of health promoters considering the reciprocal relationship between human and animal health. Future research should explore different aspects of human and non-human health, perspectives of different types of fosterers in different settings and communities, barriers to fostering, and methods that explore the role of caring for a wider range of companion animals in creating and sustaining wellbeing.