The 3B study stands for Baby, Breastfeeding and Back-to-work and aims to investigate whether, how, and under which conditions maternal work stress during the postpartum period affects maternal milk composition and infant behaviour. Data of 141 mothers and their infants is collected over two study days. The datasets consist of raw data, raw clean data, and scored data, and all data is accompanied with a codebook. For a general overview of the study at hand, see the document "3B6m_ReadMe". For a more detailed description of the study, including all materials and procedure, see the document "3B6m_MethodologyFile".