This course focuses on complex phenomena in geo-environmental engineering, where a combination of physical phenomena occurs at different scales. In-depth understanding of such multi-physics and multi-scale approaches is increasingly becoming important in many novel applications, in particular in the understanding of the behavior of triggering mechanisms of landslides, avalanches, stability of granular soils. This lecture series is aimed at academic and industrial researchers active in the fields of geo-environmental engineering, powder technology, chemical engineering, etc. The course gives a coherent view of the field, and hence is particularly suitable to researchers from various backgrounds that are in the initial and intermediate phases of their professional career. Modern multi-physics and multi-scale approaches for geo-environmental problems frequently are based on three core competences: (1) continuum mechanics for large-scale problems, (2) Discrete Element Method simulations for detailed studies of small-scale systems and (3) multi-scale analyses for bridging the small-scale behavior to the large-scale, continuum level. These competences will be taught in the course. The basic concepts and tools of each competence will be explained. This will smoothly evolve to expositions of recent research findings. The international team of lecturers is active in academic teaching as well as research. The course will start with recapitulating basic knowledge (continuum mechanics, Discrete Element Method, multi-scale analysis) to the wide target audience and then progress to highlight the latest research findings (homogenization of dry and partially-saturated granular assemblies, associated mean strain and stresses, multi-physics description at microscopic scale, stability analyses of granular assemblies, solutions of Young-Laplace equation). The topics that will be addressed include the multi-physics description at the small scales of capillary effects that result in cohesive forces at a larger scale which ultimately determine the (in)stability of granular assemblies. For such partially-saturated granular materials, it is shown how the behavior at the small-scale (capillary bridge properties that are determined by the Young-Laplace equation) can explain the macro-scale behavior, through suitable homogenization techniques (requiring a capillary stress and a statistical description of the micro-scale structure). Such analyses are complemented with Discrete Element Method simulations. The background and relevance of extended continuum-mechanical theories (higher-order, Cosserat) to the behavior of granular materials will be explained, in connection to the latest research findings. For the prediction of the avalanches and stability of granular soils in geo-environmental problems, the latest developments in the use of the second-order work approach are taught. This is connected to micro-scale modeling of granular soils.