Sepsis is a major disease entity with important clinical and economic implications. Sepsis is the hosts' reaction to infection and is characterized by a systemic inflammatory response. Because of difficulties in defining sepsis, the SIRS was introduced trying to summarize the inflammatory response in a limited set of elementary characteristics (fever or hypothermia, leucocytosis or leucopenia, tachycardia, hyperventilation). In daily practice it is essential to identify septic patients as soon as possible because early recognition results in better survival rates. However, in order to allow early detection, a more stringent description of "the septic profile" is needed. From the start, even after revision of the primary sepsis description, these definitions have caused much controversy and debate because they lack sensitivity and specificity. Conclusively, almost all patients admitted to the intensive care unit meet or develop the systemic inflammatory response syndrome. Therefore, it is difficult to distinguish patients with true sepsis from those with severe inflammation due to non-infectious causes. This review highlights the current sepsis definitions, and discusses their strengths as well as their shortcomings for daily intensive care unit practice.