This study is concerned with the introduction of a new group, Advanced Neonatal Nurse Practitioners (ANNPs), into the practice of interhospital transfer of critically ill newborn Infants. These transfers have traditionally been performed by a team led by a doctor, but ANNPs may replace doctors in this setting. Diverse methodologies are brought to bear on two main questions. First: What impact do ANNP-led transfers have on outcome? Second: How can we understand the process whereby the change to ANNP-led transport was brought about?