The Preliminary Check-list of British Marine Algae (Parke, 1953), with three subsequent lists of additions and corrections (Parke, 1956, 1957, 1959), was superseded by the Revised Check-list of British Marine Algae (Parke & Dixon, 1964). Since the publication of the latter, changes, both taxonomic and systematic, have been sufficiently numerous to warrant the present list incorporating additions, corrections and emendations.The authors take full responsibility for all the changes from the 1964 Check-list. The responsibility for the preparation of the lists of species for each Class in the 1964 Check-list was as follows: (1) Cyanophyceae, H. T. Powell; (2) Rhodophyceae, P. S. Dixon; (3) Cryptophyceae, M. Parke; (4) Dinophyceae, D. Ballantine & M. Parke; (5) Haptophyceae, M. Parke; (6) Chrysophyceae, M. Parke; (7) Craspedophyceae, M. Parke; (8) Xanthophyceae, M. Parke; (9) Phaeophyceae, H. Bladder, G. Russell, P. S. Dixon & M. Parke; (10) Prasinophyceae, M. Parke; (11) Chlorophyceae, E. M. Burrows, P. S. Dixon & M. Parke.The sequences of classes is as in the 1964 Check-list and there have been no changes in the geographical limits used therein (the coasts of Britain and Ireland or in adjacent waters, i.e. the sea area bounded by 47° N. and 63° N., 11° E. and 30° W.). Three classes (Bacillariophyceae, Rhaphidophyceae, Euglenophyceae) are still not represented and the authors would be grateful for records of marine species of these in order to facilitate their inclusion at some time in the future.The compilers welcome any comments on the Revised Check-list (1964) or the present list.