Fluids in the Earth represent one of the most active areas of research in the earth sciences. Understanding properties and distribution of fluids allows geologists to better understand complex processes related to mineral precipitation, dissolution or transformation by variety of chemical reactions. Earth scientists use various approaches to study fluids in the Earth’s interior. The most powerful are experimental mineralogy and geochemistry and the study of fluid and melt inclusions in minerals. The latter are unique sources of information concerning the composition and properties of fluids in the Earth. Composition, physical and thermodynamic properties of fluids and their capability for chemical transport are important issues, which are related to the origin of mineral deposits, magma crystallization, metamorphism and metasomatism. Thus, this session topic is relevant to the General Meeting of the IMA because the study of fluids in geological processes is an active research topic worldwide. Many laboratories and individual researchers focus their studies on experiments in fluid systems, while other s study fluid evolution based on mineral compositions and fluid and melt inclusions in minerals. The proposed session is expected to generate a high level of interest owing to the importance of fluids in a broad range of geologic processes.