Freeze casting, the directional solidification of water-based solutions and slurries, is a versatile technique for the manufacture of hybrid materials for a broad range of structural and functional applications. Still lacking for the custom design of materials for a given application are the fundamental science of structure formation and structure-property-processing correlations. In this work, a better understanding of the fundamental science of freeze casting is gained through the combination of a range of multiscale experimental techniques that are paralleled by a modelling effort. Ice-templating and self-assembly processes that determine the architecture, mechanical, and other physical properties of freeze-cast materials are observed, analyzed, and quantified in situ and post mortem. Mechanisms of nano- and microscopic structure formation in biopolymer-based systems are newly discovered, their effects on resulting properties are determined, and robust structure-property-processing correlations are derived. Advanced in parallel were freeze casting-based techniques to manufacture porous devices of complex shape, microstructure, and functionalities. Highlighted will be new material opportunities that result from the results obtained with a focus on freeze-cast hybrid materials which offer unique multifunctionalities for complex applications and the next generation of biomedical, environmental and energy-related devices.