Acute kidney injury (AKI) is a common diagnosis in daily clinical practice, occuring in virtually all fields of medicine. Critically ill patients are especially prone to the development of AKI due to frequent haemodynamic instability, multiple risk factors and, diagnostic and/or treatment complications. Severe AKI substantially prolongs the intensive care unit (ICU) length of stay, with increased risk of death. AKI is also a predisposing factor for multiple organ dysfunction syndrome and is usually a part of it. For these and other reasons, critical care nephrology plays an irreplaceable role in treating critically ill patients in ICUs. The current trend in medicine generally not only in critical care nephrology is to gather as much scientific knowledge as possible and in medicine, everything is interrelated. Further, knowledge of pathophysiology and understanding the causes of illness come in an era of increasing polypharmacy and the escalating side effects of drugs. The latter can cause conditions with the same clinical picture as immune system disorders, viruses and bacteria. Another issue is poisonings and drug intoxications, which are a daily issue in ICU settings. In short, the aetiological spectrum of disease has expanded. This book presents the basic principles in critical care nephrology and covers the epidemiology, pathophysiology, the most frequent syndromes, poisonings and conservative or invasive treatment options. The aim is to present an easily understandable overview using relevant scientific research results, along with the authors own practical clinical experience from the University Hospital of Ostrava in the Czech Republic. The authors believe that this textbook will be useful to physicians who have to make rapid diagnoses and decision making in daily ICU practice.