Fifteen new sections of genus Baccharis L. (Asteraceae, Astereae) from South America are described, four of them belonging to subgenus Baccharis: Baccharis sect. Caespitosae Giuliano, Baccharis sect. Frenguellianae Giuliano, Baccharis sect. Spicatae Giuliano, and Baccharis sect. Tucumanenses Giuliano; five belonging to subgenus Molina (Pers.) Heering: Baccharis sect. Albidae Giuliano, Baccharis sect. Divaricatae Giuliano, Baccharis sect. Effusae Giuliano, Baccharis sect. Lilloanae Giuliano, and Baccharis sect. Megapotamicae Giuliano; one belonging to subgenus Pteronioides Heering: Baccharis sect. Australes Giuliano; one belonging to subgenus Tarchonanthoides Heering: Baccharis sect. Coridifoliae Giuliano; and four sections not assigned to any subgenus: Baccharis sect. Arenariae Giuliano, Baccharis sect. Rodriguezianae Giuliano, Baccharis sect. Tenellae Giuliano, and Baccharis sect. Thymifoliae Giuliano. Three new combinations are proposed: Baccharis sect. Heterothalamus (Less.) Giuliano, Baccharis sect. Icma (Phil.) Giuliano, and Baccharis sect. Palenia (Phil.) Giuliano. A lectotype is designated for B. arenaria Baker.