It is now more than fifty years ago that the third edition of The Student's Handbook of British Mosses by H. N. Dixon & H. G. Jameson was published in 1924. Since that time the very considerable taxonomic and nomenclatural changes have been such that it is difficult for the non-expert to equate the 1924 taxa with those of today. Taxonomic revisions have resulted in the splitting of genera (and Dixon had an extraordinarily broad concept of the genus in The Handbook) and the recognition of numerous additional species especially in the Bryum capillare, B. erythrocarpum and Plagiothecium denticulatum/nemoreum complexes. As a consequence of the marked increase in interest in field bryology since the end of the Second World War numerous new species have been added to the British and Irish lists. Dixon recognised 115 genera and 625 species (in present day terms) compared with the 175 genera and 692 species described here. There is also an increasing awareness of the extent of morphological variation and the existence of taxonomically difficult groups requiring further study.

It was felt that a new moss flora was long overdue, hence the production of this book. It must be stressed that this is not a revision of Dixon & Jameson but is a completely new moss flora embodying recent ideas and views, some doubtless controversial, on the taxonomy of mosses.