Giving a definition of analgesia in ICU needs to answer several questions: Why sedation? Which drugs can we use? How can we deal with sedation? (monitoring, continuous administration, weaning...)? Two different types of sedation must be considered: treatment-sedation (status epilepticus, tetanus, intracranial hypertension...) and comfort-sedation in anxious and/or restless and/or painful patients and in those necessitating mechanical ventilation. Analgesic consumptions vary widely with diseases and their outcome, background diseases and ICU environment. Several studies have shown that pain and analgesia are frequently neglected in ICU. The authors review the different drugs in use, with their advantages and drawbacks. A particular place is reserved to regional techniques, often underused in ICU. Indications are then fully discussed, according to several specific pathological conditions. Monitoring and weaning of sedation are also discussed at the end of the review.