Light sedation, corresponding to a Richmond Agitation-Sedation Scale between 0 and -1 is a priority of modern critical care practice. Dexmedetomidine, a highly selective, central, α2-adrenoceptor agonist, is increasingly administered in the intensive care units (ICUs) as an effective drug to induce light sedation, analgesia and a quasi-physiological sleep in critically ill patients. Although in general dexmedetomidine is well tolerated, side effects as bradycardia, hypertension, and hypotension may occur. Although a general dosing range is suggested, different ICU patients may require different and highly precise titration that may significantly vary due to neurological status, cardio-respiratory function, base-line blood pressure, heart rate, liver efficiency, age and co-administration of other sedatives. This review analyzes the use of dexmedetomidine in different settings including pediatric, adult, medical and surgical patients starting with some considerations on delirium prevention and sleep quality in critically ill patients and how dexmedetomidine may contribute to these crucial aspects. Dexmedetomidine use in specific sub-populations with unique characteristics will be detailed, with a special attention to a safe use.