A variety of social systems have evolved as a consequence of competition and cooperation among individuals. Giraffe (Giraffa camelopardalis sp.) societies are an anomaly because the dearth of long-term data has produced two polar perspectives: a loose amalgamation of non-bonded individuals that sometimes coalesce into a herd and a structured social system with a ﬁssion–fusion process modifying herd composition within a community. We analysed 34 years of data collected from a population of Thornicroft’s giraffe (G. c. thornicrofti, Lydekker 1911) residing in South Luangwa, Zambia, to establish the nature of giraffe society. Our sample consisted of 52 individually recognized animals. We found that giraffe herd composition is based upon long-term social associations that often reﬂect kinship, with close relatives significantly more likely than non-relatives to establish herds. Mother/offspring dyads had the strongest associations, which persisted for years. Giraffe live in a complex society characterized by marked ﬂexibility in herd size, with about 25% of the variance in herd composition owing to kinship and sex. We suggest that giraffe herds share many characteristics of ﬁssion–fusion social systems and propose that sophisticated communication systems are a crucial component regulating subgroup dynamics.