The performance of a zeolite is dictated by its framework structure. Understanding the regular crystal arrangement is key to understanding why and how these materials function, in order to improve on the features that make them useful. This chapter covers how zeolites are classified through their framework type, how they can be described in terms of common structural features, such as building units, and how small changes to the structure can affect the performance. On the basis of several relevant examples of zeolite frameworks, the fundamental aspects of zeolite structural science are laid out. Finally, crystallographic methods for structural analysis of zeolites, such as powder X-ray diffraction, electron diffraction, and high resolution transmission electron microscopy, are summarized.