Many organisms, including humans, group together and perform collective actions such as birds forming coordinated flocks to evade predators, forage or roost. Some, as social insects, have evolved complex societies in which the unit of selection is not the individual, as in most vertebrates, but the colony. Yet, in both there is evidence of consistent behavioural variability among both individuals and groups. The study of collective behaviour - coordinated actions resulting in emergent properties at the group level - and the study of animal personality - between individual differences that are consistent over time and contexts - have progressed tremendously in the last two decades and are converging in their search for the link between individuality and collectivity, a fundamental and timely issue in biology. The GROUPIND project aims to investigate the relationship between individual personality and group personality by using ants and starlings as study organisms, both of which showing distinct collective behaviour and marked individual behavioural variability. The project will use a comparative approach to address the following objectives: (1) To characterize, also upon experimental manipulation, the composition of personalities in the group and understand how this relates to personality at the group level. Are group personalities an average of individual personalities within the group? Do they result from different distributions of individual personalities? Are there keystone individuals that exert a disproportionate influence on the group personality? (2) To understand how diversity of individual personalities contributes to decision making and to the ecological success at the group level, and how this would feed back at the individual level. By bridging two major fields of study, this project will shed new light on the ability of groups to function effectively, unravelling the consequences that personality differences can exert on social life and its evolution.