Heparan sulfate (HS) and heparin (HP) belong to the glycosaminoglycan (GAG) family, which are linear and sulfated polysaccharides. Several levels of molecular diversity allow these polymers to display one of the highest information content amongst all biopolymers and to bind and regulate, often in a specific way, the activity of numerous proteins. After analysing the structural basis of HS and HP molecular diversity, we will describe how chemists are able to exploit several of these features to produce compounds with exquisite tailor-made bioactivities and optimised pharmacological profiles, leading to promising drug candidates in preclinical or clinical studies and approved treatments.