The Multi-Level Perspective (MLP) is a prominent framework to understand socio-technical transitions, but its micro-foundations have remained under-developed. The paper's first aim is therefore to develop the MLP's theoretical micro-foundations, which are rooted in Social Construction of Technology, evolutionary economics and neoinstitutional theory. The second aim is to further identify crossovers between these theories. To achieve these goals, the paper analytically reviews the three theories, focusing on: (1) the relevance of each theory for transitions and the MLP, (2) the theory's conceptualisation of agency, (3) criticisms of each theory and subsequent conceptual elaborations (which prepare the ground for potential crossovers between them). Mobilizing insights from the analytical reviews, the paper articulates a multi-dimensional model of agency, which also provides a relational and processual conceptualization of ongoing trajectories in which actors are embedded. Specific conceptual linking points between the three theories are identified, leading to an understanding of socio-technical transitions as evolutionary, interpretive and conflictual processes.