This is a companion volume to PLANTATT, and provides for all British and Irish species a codified set of attributes for use in ecological analyses. These include information on native status, size, life form, life history, altitudinal and geographical range and habitat of 1057 British and Irish bryophyte species and a further 134 aggregates and infraspecific taxa. Much of the information is newly compiled, or generated afresh for this publication. Ellenberg values for Light, Moisture, Reaction, Nitrogen and Salt tolerance are provided for all taxa. A new classification of the life forms is proposed and applied to all taxa. Their substrates and EUNIS habitats in Britain and Ireland are also tabulated.