WHAT MATTERS? is a small book about a big subject: the long-term health and happiness of babies, young children, and their companions at home. Based on research evidence, it raises questions about what matters for all concerned. Not only parents but also grandparents, other family members, friends, and neighbours may be childcarers at home these days. WHAT MATTERS? describes a financially manageable and practical approach, with babies and young children centre stage. It explains the link between belonging and behaviour, illuminates how children learn, and suggests many companionable activities with babies and children, involving minimal expenditure. There is a focus on adults' wellbeing, especially for mothers during the first year, while looking ahead at the common ground between toddlers and teenagers. WHAT MATTERS? can make life easier for everyone, contributing to families' long-term mental health and happiness.