At least 345 bacteriophages infecting Streptococcus thermophilus starter cultures have been isolated; general characteristics include high thermal resistance, short latent periods and large burst size. Phages with such characteristics are primed to thrive in the cheese making environment, lysing bacterial cultures and generating low-quality fermented products. All S. thermophilus phages isolated to date are members of the Siphoviridae family and the Caudovirales order and appear to constitute a polythetic phage species comprising two large groups, cos- and pac-types, based on the mode of DNA packaging. Comparative analyses have shown that S. thermophilus phage genomes are similarly organized into distinct modular regions and allow the detection of a core genome region. Several PCR-based techniques have been designed to detect them in cheese whey and milk samples. Similar S. thermophilus phages are globally distributed and endemic in specific dairy environments. The biogeography of S. thermophilus phages reinforces their current classification.