Nannochoristidae (=Nannomecoptera) and Boreidae (=Neomecoptera) are traditionally assigned to the holometabolan Order Mecoptera. Both groups are key taxa and highlights in the evolution of the extremely successful Holometabola. This and an impressive number of recent studies on various aspects of Nannochoristidae and Boreidae more than justifies a new volume in the series Handbook of Zoology dedicated to these highly unusual taxa.