Linus Pauling called haemoglobin the most interesting and important of molecules. This important volume shows how X-ray crystallography was used to determine its bewilderingly complex atomic structure and to unravel the stereochemical mechanisms of its respiratory functions. It introduces isomorphous replacement with heavy atoms which led to the first protein structures, haemoglobin and its simpler relative myoglobin. Later papers deal with the stereochemistry of the cooperative effects of haemoglobin, with the relationships between the structures and impaired functions of abnormal haemoglobin, with species adaptation of haemoglobin, and with its action as a drug receptor and as an oxygen sensor. The final papers deal with amino acid repeats which act as polar zippers and their role in certain inherited neurodegenerative diseases.