The considerable demands of modern technology for new materials with specific properties have raised many possibilities for the investigation of glasses and glass-ceramics. Preparation of new glass formulations and glass-ceramics with characteristic properties, and investigation of relationships among compositions, structure, electrical and thermal properties are important for understanding the mechanisms involved in these materials. Therefore, the main objectives of the proposed research are to prepare novel ternary and multi-compositional phosphate-based glasses doped with various metal oxides and determine the correlations among the transport phenomena in both types of charge carriers, ions and electrons, present in the proposed glass and glass-ceramics systems. The reason for choosing phosphate-based glasses for investigation in this project is the extensive experience of the team members in studying this type of glasses. On the other hand, our intention is to expand the understanding of the electrical transport mechanisms by investigating two classes of novel multi-compositional phosphate glasses with specific compositions and structures. In order to accomplish this, the proposed project is divided into three main interrelated steps: 1. The first part of the investigation will be focused on the conduction mechanisms in phosphate-based glasses that exhibit mixed electronic-ionic conduction. 2. The second part includes an investigation of the influence of the mixed glass former effect on electrical processes in phosphate-based glasses. 3. The third part involves a study of the influence of controlled crystallization on electrical transport in selected model glasses from steps 1 and 2. The formation of grains of crystalline phases in a glass matrix can substantially change the electrical conductivity and dielectric properties of glass. The main idea is to perform systematic studies for understanding the charge transport (ion and electron) dynamics in glasses and glass-ceramics with different crystallinity (from fully amorphous to fully crystallized). The chosen examples will highlight the diverse nature of the electrical transport in these phosphate-based systems. In particular, the main purpose is to determine the universality of the mixed electronic-ionic and mixed glass former effects in the proposed glass systems. The motivation for the proposed research is to point out that electrical transport profoundly depends on the network structure of glass systems. The interactions between glass formers and modifiers, the formation of bonds among them are essential factors that influence the electrical properties of glasses. Beyond the connection to the central theme of the conduction mechanism, which is important from the academic point of view, the selected systems are all associated with multiple applications, such as advanced electrolytes.