Malling Olsen & Larsson's book equals or exceeds Grant's work in terms of its level of detail, and consolidates and synthesises the considerable amount of new information that has been discovered since then.

Because the publishers required only the title page of the book to be returned in order for purchasers to receive the reprint free of charge, many copies of the first printing are still in circulation.

Preceding the species accounts, an introduction covers the book's species-level taxonomy, and gives general advice on gull identification, including ageing and moult, hybrid and aberrant birds, and the effects of lighting conditions, and plumage wear and fading.

The book is particularly notable in that it is the first work to bring together information discovered during the late 1980s, 1990s and early 21st century on the identification of birds of the large white-headed gull complex.

Species-level taxonomic decisions adopted in the book are as follows: Olsen and Larsson had previously collaborated on two other volumes in the Helm series, on terns and skuas.