IssueInjury to the perineal tissues during childbirth is a frequent occurrence with most women* likely to experience perineal injury during a first birth which, in some cases, can lead to significant long-term morbidity. The techniques used to minimise perineal injury are frequently termed ‘hands on’ and ‘hands poised’ or ‘hands off’. These terms are often undefined and used inconsistently in the literature, making it difficult to identify the best available evidence to inform midwifery practice. AimThis study aimed to answer the research questions: What do midwives do to minimise perineal injury during birth and what influences their decision-making? MethodsAn ethnographic study was undertaken during 2016 in a maternity unit in the southeast of England. Data was collected through participant-observation, ethnographic and semi-structured interviews and analysed using thematic analysis, informed by the pedagogic theory of threshold concepts. Findings31 midwives participated in the study. Evidence-based decision-making to minimise perineal injury during birth was identified as a complex concept. Within the context of threshold concept theory, three main themes were identified that contributed to the complexity: troublesome language, troublesome knowledge, and troublesome environments. ConclusionsMidwifery decision-making in the context of minimising perineal injury during birth is more varied and conceptually complex than has been previously described. Identification of the various aspects of troublesomeness in this context suggests that this element of practice is a midwifery threshold concept. Addressing this within midwifery curricula and practice education to enable evidence-based decision-making is important.