This is a study of how the synergisms between cultural and structural factors, which played a major role during the historical fertility and nuptiality transition (first demographic transition or FDT), have continued to condition demographic innovations connected to the “second demographic transition” (SDT). The continuity or discontinuity from the “first” to the “second” demographic transition is studied for spatial aggregates over more than a century in two national contexts, i.e., Belgium and Spain. Special attention is paid to the role of successive secularization waves in shaping the geographical patterns of both transitions. The study also shows that the maps of the two aspects of the SDT, i.e., the “postponement” and the “non-conformism” transitions respectively, are shaped by different determinants. Explanations are offered using the “Ready, Willing, and Able” paradigm, which allows us to uncover the different conditioning and limiting factors involved. The “non-conformist” transitions (control of marital fertility during the FDT and rise of cohabitation and non-conventional family formation during the SDT) more closely mirror the history of secularization and the “Willingness” condition, whereas the fertility postponement aspect of the SDT mainly reflects female education and employment, or the “Readiness” condition. This generalization holds in both countries. However, in Belgium spatial continuity from FDT to SDT is connected to stable patterns of secularization, whereas in Spain it is linked to long standing differences with respect to female literacy and education.