Résumé : This working paper presents the theoretical and conceptual framework (hereafter referred to as the ‘TSI framework’) developed to date in the TRANSIT project as a basis for the iterative development of a middle-range theory of TSI. An earlier version thereof was used to develop a first set of ‘sensitizing concepts’, which informed a first batch of TRANSIT empirical case studies (cf. Haxeltine et al. 2014, Jørgensen et al 2014). Empirical findings were used to improve the framework and guide a second batch of case studies with a second set of ‘sensitizing concepts’ (cf. Haxeltine et al. 2015, 2015, Wittmayer et al 2015).