Streptococcus agalactiae (GBS) is a prominent global perinatal pathogen. Women in Western Australia are screened for GBS during pregnancy and receive prophylactic antibiotics at delivery if colonised. This study was the first to characterise GBS in this population and provided detailed clinical and epidemiological data. This resulted in the development of a novel diagnostic assay and elucidated prevalent serotypes and risk factors; crucial data which will inform selection of future GBS vaccine candidates. The project also resulted in the discovery of novel GBS bacteriophages with anti-bacterial activity against -70% of clinical GBS isolates, presenting a promising alternative to antibiotic prophylaxis.