This Special Issue celebrates the profound contribution the 1923 paper of Debye and Hückel  has had on the field of electrolyte solution thermodynamics. Understanding and modeling electrolyte solutions are crucial in a wide range of fields, including life sciences, chemistry, environmental studies, geology, oceanography, and material sciences, as well as chemical, biochemical, agrochemical, pharmaceutical, electrical, and mining engineering. This is evident from a recent survey on the industrial requirements for thermodynamic and transport properties . The study of electrolyte solutions has once again become a focus of research in the community of chemical engineering thermodynamics in the past 10-15 years. This trend is caused partly by the re-warmed interest of politics into carbon capture and sequestration, as in both steps electrolytes play a central role, and by the energy sectors focus on enhanced oil recovery and energy storage, which consumes considerable amounts of various ions (such as Li+, Na+) that have to be obtained from different sources by electrochemistry and biotechnology.