Group Mentality, as theorized most rigorously by W.R. Bion in his 1959 Experiences in Groups, designates the unanimous, anonymous expression of a collective will that operates beneath the level of individual conscious intention. For Bion, group mentality is not a mere aggregate of individual wishes but a sui generis phenomenon: a pooled psychic deposit to which each member contributes without awareness, and which may conflict sharply with the private desires of any single participant. The concept is inseparable from Bion’s correlative constructs of group culture and basic assumptions — the primitive, instantaneous emotional states (dependency, fight-flight, pairing) that seize a group and divert it from rational work. Freud had earlier characterized the herd as a regressive, contagion-driven lowering of individual mentality, and Bion inherits this tension while pressing beyond it: he insists that the individual is constitutively a group animal at war both with the group and with that aspect of himself that belongs irrevocably to it. Flores, reading Bion through an addictions lens, foregrounds Freud’s alarm at the group as a source of ‘contagious reduction of mentality.’ The wider depth-psychological corpus reveals that group mentality intersects persistently with questions of leadership, regression, basic assumptions, and the conflict between work-group rationality and the archaic emotional pulls that subvert it.