Book excerpt: Understanding Doctors’ Performance addresses possible reasons why doctors under-perform, covering specific areas such as education and training, physical and mental health, workload, personality, organisational culture, drug and alcohol misuse, and cognitive impairment. It draws together evidence and describes the factors (apart from clinical competence) that adversely affect performance and how they can be prevented, identified, assessed and addressed. This practical and easy to read book is invaluable for NHS managers, medical directors, chief executives and board members, along with directors of human resources in healthcare and healthcare professionals interested in the assessment of performance or the management of underperformance.