In 1931 a long-term test on the deterioration of bookbinding leathers was begun by the British Leather Manufacturers' Research Association in cooperation with the authorities in the British Museum Library and in the National Library of Wales. The bindings were examined at intervals and reports produced on their condition. The present paper summarizes the reports of R.F. Innes and others up to 1965, which have previously been published with restricted circulation. Attention is drawn to some aspects of the deterioration observed in bindings held in the British Museum Library and to mechanisms which have been suggested for the breakdown of leathers in industrial atmospheres. Comparisons are made between the relative behaviour of differently tanned leathers of which the chrome-tanned bindings, in particular, have remained apparently undamaged for over thirty years. A limited examination of some bindings (recently withdrawn from the series in London) has been undertaken, and some comments on the results so far obtained are included. The report does not duplicate previously published reviews of the literature on this subject.