Electrolyte viscosity is a macroscopic property, although its foundation lies on molecular-scale interactions between solvent and ionic species. A comprehensive understanding of viscosity behavior with respect to solvent composition, salt concentration and temperature is only possible with correct interpretations of molecular interactions and related quantities. This work introduces a new methodology for predicting electrolyte viscosity under a wide range of conditions, based on molecular, physical, and chemical properties. The general formalism is universal for aqueous and non-aqueous systems alike. Although the immediate application of the resultant model is candidate electrolytes for lithium ion batteries, other applications abound in the areas of industrial fluids, biological systems, and other electrochemical systems whose performance characteristics are tied to viscosity. Viscosity predictions are compared to experimental data for a number of electrolytes, demonstrating exceptional accuracy of predictions over wide temperature ranges and broad ranges of salt concentration. (c) 2005 Elsevier Ltd. All rights reserved.