As a significant challenge to sustainable development, climate changes require prompt and coordinated action based on a holistic approach for decarbonizing the energy system. In this framework, accounting for the sectoral interdependencies of the energy system, and their interactions with water and environmental systems is essential. The 18th SDEWES Conference in Dubrovnik, held in September 2023, served as a platform that offers experts the opportunity to exchange ideas on state-of-the-art research on the topic. This special issue of Smart Energy highlights peer-reviewed papers from the conference, covering diverse topics such as the energy-water nexus, innovative funding models for district heating, planning of thermal energy storage, and machine learning-based monitoring for HVAC appliances. These contributions highlight the importance of pursuing an integrated analysis of energy systems and provide valuable insights relevant to spearheading the energy transition.