This book proposes a feature-based design approach for three dimensional block structured components with generalized orthohedral geometry. The component is viewed as a collection of blocks connected by topological links. The geometry and topology are explicitly deﬁned. The geometry of the feature consists of an external shape and an internal shape, while the topology is modeled using a graph. The basic external shape of each block in a component is a rectangular parallelopiped which ﬁxes overall size and location of the block. Using the idea of encapsulation, families of blocks with diﬀerent internal shapes can be developed; all these internal shapes are assumed to be encapsulated in a block with rectangular external shape. The simple nature of the external shapes makes it easier to deﬁne operations like create, addition/deletion of blocks, topological connectivity speciﬁcations, etc. The internal shape provides the necessary information for geometry speciﬁc operations such as display, volume computation, etc. Dimensioning and tolerancing support is provided using a graph representation.