The advent of eusociality, a complex system comprising sterile castes that support highly fecund reproductives, is considered one of the major transitions in evolution. Since Darwin, eusociality has fascinated and confounded scientists from many fields. Eusociality has emerged independently in diverse organisms (mammals, insects and shrimps), but the underlying evolutionary principles remain elusive. For instance, the question of why eusociality evolved under such diverse circumstances, but not in other seemingly similar conditions, remains a mystery. Insects are an ideal system for studying this fascinating question since eusociality evolved independently in several groups, such as beetles, Hymenoptera and cockroaches. Blattodea (cockroaches and termites), diploid organisms with subsocial and eusocial lineages, is a particularly promising clade to reveal the prerequisites and evolutionary dynamics of eusociality, and go beyond the classical hypotheses relying on asymmetric degrees of relatedness. This proposal will concentrate on revealing the evolutionary dynamics and conditions which drove or enabled the evolution of all forms of sociality in Blattodea. We will test the shift-and-dependent-care hypothesis, which emphasises wood-eating and subsociality as initial conditions that favoured eusociality. Such a game-changing endeavour has only recently become possible due to the publication of several Blattodea genomes by the German team and others in 2018. We will test this hypothesis by contrasting multiple cockroach lineages that evolved subsociality and xylophagy to the eusocial lineage (i.e. termites). We will take advantage of the rich experience and extensive collections of the MNHN to systematically collect phenotypic data from a wide range of cockroach lineages with varying feeding habits along several levels of sociality. Building on the prior experience of both teams, we will generate novel transcriptomes and genomes for four species (wood-eating or not, subsocial or solitary). These will complement currently and soon to be available resources, to allow comparative analyses of ten blattodean species spanning five levels of sociality in five cockroach and three termite families. We will identify selective forces and investigate changes in gene families and expression networks along transitions to higher levels of sociality. All genomic data and life history traits gathered in this project will be analysed and interpreted in a unified phylogenetic context. Our data will benefit entomologists, genomicists and evolutionary biologists as, for the first time, such a resource will be available for cockroaches, a system with multiple independent lineages of subsociality. Results will address the question of whether any general principles govern the evolution of subsociality and its advancement to eusociality and which factors, such as diet or other environmental factors, drive or hinder the evolution of sociality.