IN 1928 a monograph on the “Flutter of Aeroplane Wings”, by Messrs. R. A. Frazer and W. J. Duncan, was produced at the National Physical Laboratory, summarising in a single useful volume the work that had been done by them on that subject up to that time. Since that period this work has been continued, while the associated problem of tail flutter in aeroplanes has also been the subject of study. A new volume has now been produced under the comprehensive title of “The Flutter of Monoplanes, Biplanes, and Tail Units” (Air Ministry: Aeronautical Research Committee. Reports and Memoranda, No. 1255 (Ae. 404): The Flutter of Monoplanes, Biplanes, and Tail Units (a sequel to R. and M. 1155). By R. A. Frazer and Dr. W. J. Duncan. Pp. viii +179+12 plates. (London: H.M. Stationery Office, 1931, 7s. 6d. net)), embodying results that have already been issued from time to time on wing and tail flutter under one cover. The subject is well illustrated by cinematograph pictures of some simple experiments designed to show the various types of flutter that may arise in practice, and the nature of the dynamical problems they expose. While much of the work is of a mathematical complexion, recommendations are included regarding the design of tail units and of biplane wings that should be exceedingly useful to designers. Altogether the monograph is a comprehensive record of a valuable series of investigations. It is understood that the subject of airscrew flutter, which has been under study for some time, will be produced in due course as a separate report.