Lean and Green methodologies have been the subject of case studies over the last few years, and several beneficial relationships have been found with these and with the three pillars of Sustainability: environmental, economic and social. The topic of Sustainability has been highlighted as a strategic imperative in many business discussions due to high pressure from stakeholders, and, as such, companies have invested in methodologies that contribute to sustainable development. However, smaller companies tend to face difficulties when implementing Lean-Green (LG) and sustainable practices. Therefore, the main objective of this dissertation is to understand how a framework for the systematic implementation of Lean-Green and Sustainability (LGS) aided by the integration of Industry 4.0 technologies, with a focus on helping small and medium-sized companies (SMEs) can be developed by gathering different insights through face-to-face interviews. To this end, a systematic literature review (SLR) was carried out, combined with a bibliometric analysis, focusing on the relationship between Lean, Green and Sustainability, and also with Industry 4.0. By collecting data from the Web of Science platform and using the VosViewer software, it was possible to analyse the most researched themes, the geographical regions and areas of application where research is being carried out, as well as the most used Lean and Green tools depending on whether the topic of the article was LG or LGS. The same analysis was then conducted but with the topic of Industry 4.0 incorporated, with a focus on the influence of Industry 4.0 technologies on each pillar of Sustainability. Subsequently, a qualitative study was carried out using face-to-face interviews with Portuguese SMEs. A detailed analysis of all the answers given to the proposed questions was carried out using the qualitative data analysis software WebQDA, in which it was possible to uncover the main barriers experienced in implementing these methodologies, such as resistance to change, lack of training, initial investment and uncertainties in the process. The way that different organizations approach the implementation of Lean, Green and the three pillars of Sustainability was also investigated. Industry 4.0 technologies were found crucial to monitor and improve LG actions and most companies emphasized the implementation of sustainable strategies to have higher competitive advantage and to match client’s requirements. The interviews, therefore, serve as a basis for validating the proposed framework. A four-phase framework consisting of thirteen practical steps tailored to the specific needs and constraints of SMEs was developed to facilitate and provide guidance for the implementation of Lean Green Sustainability 4.0 (LGS 4.0) methods, which can be applied to various sectors and different environmental and social contexts.