Cross-linked cyclodextrin polymers are attracting increasing interest not only from the scientific community but also from industry. These commercial polymers, discovered in the late 1960s, have applications in many fields, from pharmaceuticals to food processing, chromatography, cosmetics, membrane materials, and the environment. More recently, this class of functional polymers have been proposed as biosorbents to treat wastewater contaminated by conventional pollutants, such as metals, polycyclic aromatic hydrocarbons, phenols, and dyes, or emerging pollutants such as hormones, antibiotics, alkylphenols, and fluorine derivatives. However, although many results have been published, many questions remain not only on the chemical structure of the macromolecular networks of these polymers but also on the biosorption mechanisms involved in their use as biosorbents to treat pollutants. Solid-state NMR spectroscopy can help to answer these questions. This chapter aims to summarize and discuss the role of solid-state NMR spectroscopy in characterizing the structure of cross-linked cyclodextrin polymers and the interactions involved in biosorption using the state of the art and our own research results obtained over 25 years.