The second demographic transition (SDT) refers to a shift in family and fertility patterns in Western societies, characterized by sub-replacement fertility, non-marital cohabitation, and a decline in marriage as a primary route to procreation. This transition began in the 1950s with rising divorce rates, declining marriage ages, and increasing cohabitation. By the 1980s, over 40% of births in France and the UK occurred outside of marriage. The SDT is distinct from the first demographic transition, which was driven by economic development and material needs, and is instead linked to higher-order, non-material needs such as individual autonomy and self-realization. The SDT has been criticized for being a Western phenomenon, but it is now evident in Central and Eastern Europe and Southern Europe as well. The SDT is associated with a shift in societal values, including a move away from traditional family structures and toward more individualistic and expressive lifestyles. The SDT has significant implications for population aging, fertility levels, and the need for immigration. The SDT is not a single transition but a complex process with varying patterns across different regions and social groups. The SDT is influenced by factors such as education, economic conditions, and cultural changes, and it is not a uniform process but rather a diverse and heterogeneous phenomenon. The SDT is a major shift in demographic history, with far-reaching implications for family structures, fertility rates, and societal values.The second demographic transition (SDT) refers to a shift in family and fertility patterns in Western societies, characterized by sub-replacement fertility, non-marital cohabitation, and a decline in marriage as a primary route to procreation. This transition began in the 1950s with rising divorce rates, declining marriage ages, and increasing cohabitation. By the 1980s, over 40% of births in France and the UK occurred outside of marriage. The SDT is distinct from the first demographic transition, which was driven by economic development and material needs, and is instead linked to higher-order, non-material needs such as individual autonomy and self-realization. The SDT has been criticized for being a Western phenomenon, but it is now evident in Central and Eastern Europe and Southern Europe as well. The SDT is associated with a shift in societal values, including a move away from traditional family structures and toward more individualistic and expressive lifestyles. The SDT has significant implications for population aging, fertility levels, and the need for immigration. The SDT is not a single transition but a complex process with varying patterns across different regions and social groups. The SDT is influenced by factors such as education, economic conditions, and cultural changes, and it is not a uniform process but rather a diverse and heterogeneous phenomenon. The SDT is a major shift in demographic history, with far-reaching implications for family structures, fertility rates, and societal values.