Postpartum depression is common, affecting 10-15% of women, and increases risk for suicide. Postpartum psychosis is rarer (approximately 1/1000 women), but is a psychiatric emergency. Women with postpartum psychosis or severe postpartum depression need care in hospital to protect their health, and the health of their families. Currently in Canada, these hospital stays separate women from their babies, which can be traumatic for mother and baby. In other countries, Mother-Baby Psychiatric Units (MBUs) admit both mother and infant for care. This study will investigate whether MBUs are suitable for Canada, or whether another model of care would be better for Canadian families. To do this, we will conduct three sub-studies. Sub-study 1 will amplify women’s stories of the experience of a hospital stay for postpartum mental illness in Canada. Sub-study 2 will describe the frequency and predictors of hospitalization for postpartum mental illness. Sub-study 3 will provide a rich picture of the MBU model of care through a case study of five international MBUs. By understanding how to best meet the needs of women and families living with serious postpartum mental illness, we aim to improve mental health outcomes across generations.