This chapter examines the different types of social forms found in insect taxa, from the relatively simple social behaviors of aggregating species, to the complex cooperative and altruistic interactions that frame cohesive communal and eusocial groups. The diverse patterns of insect social living are considered within an inclusive fitness framework, to explore the fundamental question of why social species can be so successful, but sociality itself is taxonomically rare. To answer this question requires consideration of the ecological, life history and behavioral drivers of social living, including the roles of cooperative group defence, alloparental care, cooperative foraging, and group homeostasis. The evolution of cooperative sociality does not form a single path from group living to eusociality. Instead, its diverse forms represent different evolutionary solutions to those ecological problems that can best be solved by living socially.