Around 45% of families in the UK are now one-child families, increasingly by choice but also due to factors outside parents' control, such as the cost of living, infertility, relationship breakdown and birth trauma. Whatever their circumstances, parents are often told that their child will struggle with friendships, be lonely, or be spoiled, and they may frequently be asked if they are having more children, which can be intrusive and upsetting. Why One-Child Families Matter looks at the evidence surrounding one-child families, showing how childhood experiences and outcomes are complex and shaped by much more than the number of siblings a child has. With strategies to support only children, and contributions from hundreds of one-child families, it reveals the ways that one-child families can thrive.