Identification of the underlying disease condition is the foundation of successful and curative therapy. In stable patients, this process can be summarized in a single algorithm (Fig. 1.1). In the critically ill patient, however, acute life-threatening complications often interfere with this essential algorithm. At times, unstable vital functions result in the sole focus being on resuscitation, at least during the early management of the critically ill. It requires in-depth experience in and knowledge of both diagnostic workup and resuscitation to focus on the appropriate aspect of care at the right time. Inappropriate focus on either of the two pillars of intensive care inevitably results in inadequate treatment and may impair the chances of subsequent favourable functional recovery.