The postpartum period represents a time of significant physical, psychological, and social changes where mothers face numerous specific stressors and demands. They may experience substantial postpartum stress—a specific form of stress triggered by postpartum stressors (events, situations, or daily challenges which cause discomfort) occurring within the first postpartum year. Most significant stressors during this period can be categorised into parenting roles, tasks, resources, and relationships, which more specifically refer to infant care, physical changes and overload, lack of sleep, lifestyle changes, returning to work, isolated motherhood, changes in body and sexuality, and breastfeeding. Global prevalence rates ranging from 8% to 68% point to postpartum stress being a widespread health issue. Additionally, prolonged exposure to stress can lead to many adverse effects, such as health problems in mothers and infants and a strained mother-infant relationship. Postpartum stress is complex as it is shaped by various biological (e.g. neuroendocrine, genetic and epigenetic, obstetric, maternal health), psychological (e.g. pregnancy plans, maternal personal characteristics), and social (e.g. sociodemographic, infant characteristics, social support) factors. Unfortunately, for years, it was widely unrecognised or investigated only as a risk factor for other peripartum difficulties; however, addressing and mitigating postpartum stress is crucial for improving outcomes for both mothers and children. This chapter puts postpartum stress into focus by examining postpartum-specific stressors, clinical presentation, prevalence and course, biopsychosocial risk factors, consequences, and assessment methods, followed by a biopsychosocial framework of postpartum stress that can guide researchers and clinicians in alleviating the personal and global burden of postpartum stress.