As our society grows more interconnected through digital and physical platforms, the number of ways to carry out work-related tasks has increased quickly. Work may no longer be linked to a physical space. Many consider the productive environment created by the COVID-19 lockdowns as clear evidence that hybrid work may be successful, hence advancing digital transformation trends [1]. However, there are still several gaps that need to be tackled to address the challenges of hybrid work, particularly in terms of understanding the implications of hybrid work to personal wellbeing, job performance, and energy challenges. To address these challenges, an inter-disciplinary project has recently been set up, with funding from BELSPO (The Belgian Science Policy Office): Sustaining Hybrid Work (SUSHY). This Ph.D. thesis responds to the third track of the SUSHY project, particularly addressing the challenges of hybrid work from the perspective of energy performance. Hybrid work refers to the possibility for the worker to combine multiple locations to carry out their work [2]. The current scientific understanding of hybrid work is fragmented, making it challenging for decision-makers (policymakers, unions, and employers) to make fully informed decisions supporting a sustainable hybrid work environment. Some studies emphasize the environmental impact of hybrid work in terms of energy needs and associated carbon emissions due to heating, cooling, lighting, and other (shorter) journeys occurring during hybrid working days. However, the exact magnitude of such energy "gain" is complex to estimate, and a comprehensive assessment of the actual effects of hybrid work practices remains uncertain. Very rarely, the energy use patterns (i.e., office energy use, household consumption, and mobility) have been evaluated comprehensively, also in terms of the temporality of their occurrence [3] [4]. Likewise, a question remains on how hybrid work practices can contribute to shape tomorrow’s workplaces to sustain a consistent work environment considering the use of the energy that is necessary to operate buildings. In terms of the methodology, the study first applies a large-scale employee survey to characterize hybrid work and measure the effects of hybrid work practices on energy demands in Belgium. The workers of the different companies selected will be recruited for the large-scale survey via a link to a web survey sent out via their company email and/or their trade union representative. Afterwards, case studies will be conducted in a selected set of Belgian companies. The case studies will rely on semi-structured interviews with key people (HR director, Facility manager, CFO…) offering an access to existing data on energy demands (i.e., bills, consumption monitoring, etc.). Then, the study will apply a diary research method combining both quantitative and qualitative elements. The diary instrument will integrate structured questions and will include regular measurements of energy demands. The objective is to unveil the reasons leading to lower or higher energy demands regarding the implementation of hybrid work. This Ph.D. thesis is a part of a large inter-disciplinary project called “SUSHY: Sustainable Hybrid Work” supported by BELSPO (The Belgian Science Policy Office) in the context of Brain-Be 2.0 – Belgian Research Action Through Interdisciplinary Networks (2018 -2023). The project partners of this project are UCLouvain-LouRIM, ID-VUB, UCLouvain-iMMC, and UCLouvain-LAB.