The emergence of scientific and technological fields can follow three distinct technological trajectories: 1) a major disruption with regard to the previous technologies (e.g. biotechnologies which emerged through “destructive creation” among the life sciences); 2) a cumulative regime where previous and highly specialized knowledge is accumulated and extended; 3) a hybridizing regime. We define a hybridizing regime as a regime within which scientific and technological novelty comes from the unique combination of different bodies of knowledge belonging to previously distinct fields. Many authors consider that the expansion of nanotechnologies occur under a hybridizing regime. HybridTrajectories aims at characterizing the technological trajectories under a hybridizing regime, which has been so far less explored than the destructive creation or the cumulative regime. It explores the scientific, organizational and institutional determinants of the technological trajectories in the hybridizing regime. For this purpose, the project focuses on the professional trajectories of scientists who are deeply involved in the creation of a scientific field. In deed, these professional trajectories provide empirical markers for the emergence of new fields, such as the importance of hybridising vs. disruption and continuity; mobility between field, knowledge persistence and irreversibility. HybridTrajectories applies this approach to nanotechnologies, a field which is often considered to bring a scientific and industrial revolution by hybridizing several existing disciplines (physics, electronics, biology, and cognition) and technologies. Thus nanotechnologies appear as a good observation point to develop a more general analysis on knowledge production dynamics under a hybridizing regime. The project’s contributions are twofold.First, the characterization of the hybridizing regime through professional trajectories fills a theoretical gap. In deed, it provides a mid-range approach whereas current social science analyses focus rather on the macro- and aggregated level (using e.g. bibliometric indicators) or on the micro-level (studying e.g. laboratory work). Secondly, the project also brings new insights to various stakeholders in the nanotechnologies (scientists, and policy makers). By analysing the social processes by which a new field emerges, HybridTrajectories enables to rule out deterministic explanations of technological trajectories and to discuss the various choices underlying public action. The project proposes a challenging approach based on an interdisciplinary study (sociology, economics, and management) and on an international comparison (between France and Korea). It is organized around the four main dimensions of the professional trajectories in the sciences: publications, networks, transformation of work and disciplinary identities, and the institutional work of scientists (that is their actions to create and maintain institutions in their field). The comparison between France and Korea appears particularly appealing: the two countries share many similarities regarding their science and innovation systems and the current state of nanotechnologies. However, nanotechnologies expand much faster in Korea than in France. HybridTrajectories relies on a strong partnership between three research units (PACTE, GEM, and IREGE) which bring their complementary disciplinary expertises to the project. PACTE will coordinate the project. The project coordinator and the workpackage leaders have already worked together on interdisciplinary research projects related to dynamics in science, technology and innovation.