Large organizations are responsible for a significant amount of GHG emissions, and recent estimates suggest that the potential contribution of large organizations to global warming over the next 100 years will even increase. Within this framework, a worthy issue for environmental psychological research is the investigation of the factors promoting or hindering the transition to more sustainable everyday behaviours and practices in the workplace. The study presented here is part of a larger EU-FP7 funded research project, currently in progress, which groups together seven different research teams from six different European countries: Spain, Italy, Romania, Sweden, The Netherlands, UK. In this case, we will present the results of a qualitative study, carried out with the aim of assessing the existing everyday practices and behaviours in the workplace, which have an impact on the level of greenhouse gas emissions, in a large Italian company in the energy production sector. The environmentally-relevant everyday practices in organization considered referred to three main categories of organizational practices: 1) Consumption of materials and energy; 2) Waste generation and management; 3) Organization-related mobility. Three different sources of data and information were used: a) interviews with key-informers situated at different levels of decision-making; b) focus groups; c) analysis of organizational documents. All the material gathered was subject to thematic content analysis procedures, using Computer Assisted Qualitative Data Analysis Software (CAQDAS), specifically the ATLAS.ti software. Results from the three data sets converge in showing the presence of main barriers (e.g.: ‘Time is a barrier for sustainable mobility’; ‘There is no automatic switch off of lights at work’) and drivers (e.g.: ‘People save energy at home to save money’; ‘The organization encourages policies of consumptions reduction’) at both the individual and organizational levels. These identified factors are incorporated into a theoretical model, predicting sustainable individual and collective practices in the workplace. This model will be subsequently tested in a quantitative study, conducted through standardized psychometric tools. The implication of the findings will be discussed, in light of the possible organizational strategies and policies in order to enable transition to a more sustainable working environment and working practices.