Studies devoted to individual and collective memory have evolved in a compartmentalized way for more than a century. We recall the most emblematic historical works of two distinct visions of memory: those of the experimental psychologist Hermann Ebbinghaus who measured memory, on himself, from lists of meaningless syllables, and those of the sociologist Maurice Halbwachs for whom any act of memory is a social act. Since the beginning of the years 2000, the social turn in life sciences and, more rarely, the opening up of sociologists and historians to the life sciences have tended to bring these hitherto compartmentalized currents together. The Programme 13-Novembre has seized upon a diversity of research tools on memory by applying them to a traumatic event in French society: the attacks of 13 November 2015 in Paris and its immediate suburbs. The main objective of this program is to better understand the links between individual and collective memory in the construction of these memories related to this traumatic event. This research is fundamentally transdisciplinary—i.e., developed by researchers from different disciplines—and longitudinal over 12 years to understand the evolution of memories over time. Our studies focus on people who were closest to the traumatic event—and likely to develop posttraumatic stress disorder—and on those who were further away but who are more representative of the general population. We present some of the results, derived from data collected in studies of the program that feed our advocacy for new memory sciences.