Bacteriophages, viruses that infect bacteria, are the most abundant biological entities on Earth. Siphophages, accounting for ∼60% of known phages, bear a long, flexible tail that allows host recognition and safe delivery of the DNA from the capsid to the cytoplasm of the infected cell. Independently from their host (Gram positive or Gram negative) and the nature of their receptor at its surface (polysaccharide or protein), the core tail architecture of all caudophages and of bacterial phage-derived contractile injection systems share the same structural organisation and are thought to be homologous. Here, we review the recent advances in the structure, function and assembly of the core tail architecture of siphophages.