The integration of sectors for more sustainable systems and processes provide a multi-disciplinary research domain to which researchers are contributing with intense motivation in the context of urgency for addressing global climate change. The 26 papers in the current special issue of the 12th Conference on Sustainable Development of Energy, Water and Environment Systems represent a pursuit of excellence for leading related advancements. This editorial contains a review of these advances with a focus on the themes of effective valorisation of bioenergy resources, energy-water nexus in wastewater treatment processes, optimized local energy supply for efficient and clean systems, solar energy technologies for the energy transition, and technologies for efficient combustion and electric transport. Other themes are alternative and cross-cutting technologies for the energy system in addition to analyses of thermal energy recovery and heat transfer. Significant contributions under these themes relate to biomass residues and biogas upgrading processes, novel renewable energy and performance comparisons in the wastewater sector, efficient micro-cogeneration, polygeneration and load sharing approaches, clustering techniques in district heating networks as well as hybrid and concentrated solar power systems. Control strategies for latent energy storage, aging processes in battery packs, engine knock occurrence and coupled numerical engine modelling, fuel blends with nanoparticle additives, utilization of flue gas, soot formation in plastic waste pyrolysis, high altitude wind energy systems as well as exergy analyses for heat and cold recovery and reverse electrodialysis are other key contributions. The advances are expected to enable more sustainable energy conversion and management processes in a time when an integrated approach is nothing less than essential to maintain a coherent and liveable Planet.