Building Blocks project seeks to evaluate the Family Nurse Partnership Programme in England. It is a randomised controlled trial with a parallel economic evaluation and modelling study. The Family Nurse Partnership is an intensive, nurse-led home-visiting programmed especially designed for young, first-time parents and their children who are living in areas of socio-economic deprivation. The study aims to evaluate the effectiveness of the FNP within three domains: pregnancy and birth, child health and development, and parental life course and self-sufficiency. In addition, the cost-effectiveness of the intervention compared with existing child services will be assessed.