Soft matter systems include mixtures of colloidal particles, globular polymer coils, and stiff polymeric or colloidal rods, as well as amphiphilic molecules, familiar, from everyday life, as soap. Such systems can be experimentally prepared and are well characterized. A statistical description using idealized models proves to be fruitful, and allows determination of the structural correlations and phase behavior in bulk and at interfaces. Within the framework of classical density-functional theory, we present a geometry-based approach to such models, and derive demixing behavior in bulk, similar to the liquid-gas transition, and wetting near a hard wall. We speculate that the enhanced miscibility of oil and water upon addition of soap can be understood from the tadpole shape of the soap molecules.