The concept of the “Second Demographic Transition” (SDT), introduced by Ron Lesthaeghe and Dirk van de Kaa in 1986 has profoundly influenced research on family and fertility behaviour. It can be argued that presently, it constitutes “the” mainstream concept among population scholars dealing with demographic change in European societies.

The SDT entails on the one side a macro-level view of societal development that stresses the importance of ideational changes in bringing about certain demographic behaviours such as single living, pre- and post-marital cohabitation, delayed fertility, high prevalence of non-marital fertility and high rates of union disruption. This developmental view is subject to debate, in particular with regard to the possible persistence of the differences between the patterns of family and fertility behaviour in north-western Europe - the cradle of “new” family patterns – and southern European societies on the one side and central and eastern European countries on the other side. This debate has often been framed as whether family and fertility behaviour will converge to a common “standard”, as set by societies that are considered to be most advanced in the SDT, i.e. Scandinavian countries.

On the other side, on the micro level the diffusion of the SDT concept has focussed attention on the importance of subjective evaluations (especially, of values) in shaping differential family and fertility behaviours within societies. This is of course connected to the macro-level developmental idea of SDT (a higher share of the population sharing “new” values in certain countries may imply a higher share of the population exhibiting “new” behaviours), although it has a more general applicability. Long-term persistence of old behavioural patterns or resistance to new behaviours can be connected to the reproduction of certain values. In addition, the connection between values and behaviour may be not direct and may vary across contexts.

The working group on the SDT addressed, among others, the following questions.

• How has the concept of SDT evolved over time both in the work of the original proponents and in scientific use more general? What are the advantages or disadvantages of using the notion of "transition" to describe changes in the pattern of family formation?
• What is the evidence of macro-level diffusion of SDT behaviours? Is there only one line of evolution? What are the persistent differences and why do they persist?
• Are there alternative “grand” theories on family and fertility behaviour in Western Societies?
• What is the impact of values on family and fertility behaviour? What is the new evidence that can be given with new data collection efforts?
• Has the impact of norms on fertility and family behaviour really diminished (or vanished) in Western societies?
• What is the relationship between the notion of SDT and that of lowest-low fertility? Are they alternative concepts?
• What are the consequences of new behaviours?

Activities of the Working group included in 2001, a EURESCO conference chaired by Hans-Peter Kohler and Aat Liefbroer, sponsored by the European Science Foundation and the European Union, on “The Second Demographic Transition. Family and Fertility Change in Modern Societies: Explorations and Explanations of Recent Developments”. Although the WG had not officially started by then, this conference can be viewed as the informal starting point of the WG.

In 2003, a second EURESCO-conference was organised, from 19 – 24 June in Spa, Belgium. It focusud on “Implications of Family and Fertility Change for Individuals, Families and Society”. As the title makes clear, this conference aimed at the consequences of recent demographic change for all sectors of society. Invited speakers not only included demographers, but economists and sociologists as well.

Also in 2003, a special session at the European Population Conference in Warsaw was organised, a debate on the concept of SDT with one or more prominent proponents and one or more prominent opponents of the concept. It was a good opportunity to bring the WG to the attention of the wider demographic community.

The Working Group stopped its activities in 2005.