The COVID-19 pandemic is creating global disruption and every area of life is touched, including breastfeeding. Psychological stress during the pandemic affects prolactin release in nursing mothers, which impacts lactogenesis stimulation and milk secretion initiation. Many motivated new mothers in urban areas of Indonesia failed to reach public health goals for breastfeeding, highlighting the need to identify risk factors. Since psychological stress is associated with blunted prolactin responses, this book is based on our research to identify associations of psychological stress during the COVID-19 pandemic against serum prolactin levels in young Indonesian nursing mothers within an urban setting. This book is prepared to help students, lecturers, midwives, nurses, breastfeeding consultants, or practitioners to develop new knowledge in prolactin serum levels in young breastfeeding mothers with psychological stress during the COVID-19 pandemic.