The glycosaminoglycan heparin has been used in the clinic as an anticoagulant for more than 50 years. A fully characterized sequence in native heparin is known to be responsible for this activity. However, heparin is a complex polysaccharide, which has an array of properties that are unrelated to its anticoagulant activity. Recent research has provided us with an increased understanding of the specific structural requirements for the various actions of heparin, indicating that it might be possible to create 'tailor-made' sequences based on the heparin template to isolate specific therapeutic activities. This research should provide the basis for novel drug treatments for a range of diseases, including cancer and various inflammatory diseases.