This book presents statistical physics methods based on self-consistent field theory for describing the thermodynamic properties of ion-molecular systems, including electrolyte solutions, ionic liquids, polymeric ionic liquids, and metal-organic complexes. The methods are applicable in both the bulk and at interfaces, taking into account the molecular structure of these systems. The book also provides a comprehensive analysis of the current state of art on statistical field theory for ion-molecular systems. It is primarily intended for researchers and graduate students in physical chemistry and condensed matter physics, as well as for physical chemists, physicists, and engineers interested in molecular system theory and simulation. By presenting these approaches, the book aims to enable readers to solve various problems in physical chemistry and electrochemistry using the methods described. The authors attempted to focus on specific issues and provide the necessary theoretical background. The book includes a mathematical introduction that readers can consult if they need clarification on any mathematical concepts or details omitted in the main text. In order to read the book, it is recommended that readers have a basic understanding of calculus, linear algebra, and probability theory, which can be acquired through standard university courses.