The demands on emergency departments are rising worldwide. Simultaneously, the scope of practice of emergency medicine continues to expand. This is fuelled by an ageing population, complex medical presentations, rising patient expectations, diffculties with access to primary care facilities, and the desire for second opinions in the case of diagnostic delay or failure in primary care settings. Diagnostic failure is the leading source of clinical complaints and of medico-legal litigation involving emergency departments. The emergency practitioner not only needs to be profcient in the evaluation of common highstakes conditions, but also has to be aware of malignant disease and rarer conditions that can present to the emergency department and facilitate their diagnosis and subsequent management. This ensures more effective communication with specialists receiving referrals. In particular, the new diagnosis of cancer is increasingly being made in the emergency setting. Once the correct diagnosis is made, it is recognised that treatment protocols and referral pathways can vary widely and that local guidance is more appropriate. Diagnostic accuracy, however, remains a universal common concern. This book aims to provide the emergency practitioner with diagnostic aide-memoires and checklists as part of the front-line diagnostic armamentarium.