This deliverable articulates the just transition concept and related definitions and provides the foundations for the methodological approach to be undertaken in FITTER, thus guiding the data collection process. At the core of this deliverable is a literature review of theories, approaches and indicators of social justice and of equality. Drawing on various disciplines (including philosophy, sociology, law, economy and political science) and schools of thought, the deliverable also examines how the concept is articulated in academic and public debate. To fully explore the multiple aspects of the just transition, the analysis also considers different drivers of inequality in contemporary European Union (EU), with structural and spatial inequality at its focus. The twin transition concept is also operationalised through in-depth scrutinisation of the ‘green’ and ‘digital’ aspects of the socio-economic shifts, with a further examination of their impact on inequalities in four sectors: Energy; Transport; Building & Housing; and Food & Agriculture.