The following sections are described and illustrated in this book: Agaricus sez. Bivelares, Agaricus sez. Chitonioides, Agaricus sez. Xanthodermatei, Agaricus sez. Hondenses, Agaricus sez. Sanguinolenti, Agaricus sez. Bohusia, Agaricus sez. Nigrobrunnescentes, Agaricus sez. Lanosi, Agaricus sez. Agaricus, Agaricus sez. Rarolentes, Agaricus sez. Spissicaules, Agaricus sez. Subrutilescentes, Agaricus sez. Arvenses, Agaricus sez. Minores. The majority of the species are sequenced and represented with illustrations that come from original description of the species.