In this chapter an overview is given in which way framework-like crystalline compounds can be regarded as nets, how a net is derived out of a particular crystal structure, what nets actually are, how they can be appropriately described, what the characteristics of nets are, and how this topological approach helps to categorize framework compounds. Finally the term reticular chemistry is explained and a number of examples are given how the topology-guided approach opens up new possibilities to intentionally develop new framework structures on a rational basis.