Interfaces are common microstructures and occur in natural and synthetic materials on the local to mesoscopic lenght scale, like ferroic twin walls or interfaces between amorphous and crystalline material. Individual interfaces can be thin walls extended over a few unit cells or even thicker walls up to several 10000 Å. Walls show distinct physical properties and can therefore influence the macroscopic materials properties considerably. Examples of wall structures and their local features related with ferroic, non-ferroic and biomaterials are presented in this work.