Modular design separates complex products in parts which can be developed independently from each other. Nevertheless, all components should be composed to a product. Aiming at offering a broad variety of individual products, modular design enables to regard single components of a product separately to offer varieties. Sub-products can be analyzed easier, optimized and adapted to industry standards. At the same time individuality is increased. Building-blocks are closely related to modular design, depicting the increase of product variety by composing single product components flexibly. Modular design is only one approach to offer variability and is closely related to communication and information management as well as software infrastructure.