Sleep disorders are frequent (18%–23%) and constitute a major risk factor for psychiatric, cardiovascular, metabolic or hormonal co-morbidity and mortality. Low social status or income, unemployment, life events such as divorce, negative lifestyle habits, and professional requirements (e.g., shift work) are often associated with sleep problems. Sleep disorders affect the quality of life and impair both professional and non-professional activities. Excessive daytime drowsiness resulting from sleep disorders impairs efficiency and safety at work or on the road, and increases the risk of accidents. Poor sleep (either professional or voluntary) has detrimental effects comparable to those of major sleep disorders, but is often neglected. The high incidence and direct/indirect healthcare and welfare costs of sleep disorders and poor sleep currently constitute a major medical problem. Investigation, monitoring and strategies are needed in order to prevent/reduce the effects of these disorders.