Any science, including developmental science, functions within a broad set of concepts that generally go unnoticed during day to day research activities. These background ideas constitute the conceptual framework or context within which day-to-day research activities operate. A conceptual framework that has until recently dominated virtually all of science has been termed the Cartesian-Split-Mechanistic scientific research paradigm. In a number of scientific fields, including developmental science the inadequacies of this paradigm have become crystal clear, and new data has increasingly been highlighting these inadequacies. In this chapter this research paradigm is compared and contrasted with a newly emerged alternative scientific research paradigm termed the Process-Relational and Relational-Developmental-Systems paradigm. It has been said that science is taking a relational turn. This chapter explores the nature of this turn, and its implications for theory and methods, especially in developmental science.