The theory and empirical basis of the demographic transition includes the important role played by mortality declines in generating a societal shift from high mortality and high fertility to low mortality and low fertility. In particular, it is the improved survival of children into adulthood that initially produces increasingly large populations with a very young age structure. Because the level of childhood mortality is strongly linked to fertility levels (Angeles, 2010; Becker and Barro, 1988) and adult mortality rates, the definition of a high mortality country used in the IIASA–Oxford survey reported in this book is in terms of the level of childhood mortality, that is, the probability of death before the age of five (5q0 in the life table designation). In accordance with recent practice at the World Health Organization (WHO) and UNICEF in monitoring progress toward the Millennium Development Goals, we use a cutoff point of 40 deaths before age 5 per thousand live births to designate a country as having high mortality (Hill et al., 2012). In 2010, the under-5 mortality rate exceeded 40 in one-third of the 193 member countries of United Nations (UN), and in only one of these countries did life expectancy at birth exceed 70 years (Azerbaijan, e0 = 70.1) (United Nations, 2011a). Despite its relatively low under-five mortality rate (estimated at 0.025 in 2011), Botswana is also considered here as a country with high mortality because its life expectancy is estimated at 53 years (United Nations, 2011a). The geographic distribution of these countries is shown in Figure 6.1, while Table 6.1 lists all 65 high mortality countries, along with current estimates of life expectancy, child mortality, and the change in life expectancy between the periods 1995–2005 and 2005–2010. As shown, high mortality countries include all of sub-Saharan Africa except the island nations of Cape Verde, Mauritius, Mayotte, and Réunion. Most of South Asia meets the criterion of high mortality, including the populous countries of India, Pakistan, and Bangladesh. Many demographers have, over the last 50 years, predicted a general convergence worldwide toward low mortality and fertility resulting in higher levels of life expectancy.