The great increase in interest in gull identification since the publication of the first edition (and the author's series on that topic in British Birds) has helped bring much new information to light. As a result some revision was made to almost every text page and most of the identification drawings were improved in some way; in addition, changes were made to many of the distribution maps. These revisions and improvements were often quite minor, but others were substantial and important (see the author's Introduction). Until recently gulls were widely regarded as a difficult group and identification and ageing was often inaccurate or uncertain. This was largely due to the complexities of immature plumages, which of necessity were generally unrepresented in standard field guides. Birdwatchers need no longer be deterred or confounded by that deficiency. The book offers them the opportunity to advance their skill in field identification by accepting the challenge rather than shrinking from the difficulties.