The present invention provides a multivalent immunogenic composition having 15 distinct polysaccharide-protein conjugates. Each conjugate consists of a capsular polysaccharide prepared from a different serotype of Streptococcus pneumoniae (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 22F, 23F or 33F) conjugated to a carrier protein, preferably CRM197. The immunogenic composition, preferably formulated as a vaccine on an aluminum -based adjuvant, provides broad coverage against pneumococcal disease, particularly in infants and young children.