Structural determination is an essential component for the discovery of new compounds, and single-crystal X-ray diffraction (SCXRD) is recognised as the most reliable technique. Since SCXRD requires high-quality single crystals for analysis, it does not apply to non-crystalline compounds. The crystalline sponge method (CSM) provides the opportunity to analyse target compounds (guest) without crystallisation by using a pre-crystallised porous coordination network (crystalline sponge), which absorbs guest molecules into their pores. The guests inside the pores of the crystalline sponge are organised through host–guest interactions and are then observable by SCXRD analysis. This review will discuss applications of CSM along with a brief history and provide an overview of the range of crystalline sponges developed to date.