The findings of the Birthplace in England Research Programme showed that midwife-led units are providing the safest and most cost-effective care for low risk women in England. Since the publication of the updated National Institute for Health and Care Excellence (NICE) intrapartum guidelines, there is likely to be even more interest in the development of midwife-led units to promote birth outside obstetric units (OUs) for low-risk women. Professional bodies, policy makers and trusts have focused their energies on alongside midwife-led units (AMUs), which are seen to provide the 'best of both worlds' between home and an OU. Between 2012 and 2013, we carried out a study of the organisation of four AMUs in England and the experiences of midwives and women who worked and birthed there. Learning from their experiences, this article presents five key factors which help make AMUs work.