Life expectancy of a human population measures the expected (or average) remaining years of life at a given age. Life expectancy can be defined by two forms of measurement: the period and the cohort life expectancy. The period life expectancy represents the mortality conditions at a specific moment in time, in comparison to the cohort life expectancy, which depicts the life history of a specific group of individuals (born in the same year). Period life expectancies are frequently utilized when assessing and monitoring the health status of a population over time. Currently, the life expectancy of the Western world population is much greater than in prior decades. The dramatic increase over the last century is considered as one of the great achievements of modern societies. Between 1970 and 2009 the average length of life in the old EU member states increased from 68.7 to 78.0 among men and from 74.9 to 83.5 among women. Similar trends were witnessed among the elderly. Although there are many differences in the health service organization, national wealth, culture and associated individual behaviours between these countries, within a broader European perspective the upward trends are remarkably alike. In the first half of the twentieth century eradication of infectious diseases caused unprecedented improvements in mortality, particularly at young ages. As the risk of dying from infectious diseases was reduced, those saved from dying at younger ages survived to middle and older ages. A second wave of mortality improvement was achieved mainly at the adult life. Since the 1970s ischemic heart disease mortality has decreased in most Western countries contributing to the majority of the declines in age-specific death rates. It has been suggested that the decline in cardiovascular disease mortality is due to the combination of better treatment and changes in risk factors such as: lower blood pressure, reduced tobacco consumption, diets containing lower cholesterol, and increased physical activity within the population. There are of course more distal influences that contributed to the gains in overall mortality. The most important elements include increasing welfare, greater access to and better quality of health care, rising living standards and improvements in the level of education. In comparison with mortality, health is difficult to measure and estimates of population health are usually based on self-reported survey data. There is no single indicator that summarizes the health of a population thus no harmonized way of measuring health.