Bacteria within the genus Streptococcus have evolved to become exquisitely adapted to the colonization of humans and animals. These bacteria predominantly live in harmony with their hosts, but all have capacity to cause disease should prevailing conditions allow. Streptococci express a myriad of colonization and virulence attributes that promote their survival at a variety of ecological sites. Many of these factors are surface-expressed adhesins that exhibit conservation at structural or functional levels across the genus. This reflects the importance of adherence interactions with a multitude of host substrata, such as epithelia or extracellular matrix components, to streptococcal survival. Other important factors are more restricted in their distribution, often conferring pathogenic capabilities associated with immune evasion or host tissue destruction. Evidence suggests that dissemination of these streptococcal attributes has frequently been driven by the movement of genetic material via lateral gene transfer, reflecting ecological pressures. Such recombination events have simultaneously facilitated extensive diversification, resulting in distinct tropisms at the species- or strain- level. These generic determinants offer significant potential as targets for combating streptococcal disease. However, this will depend upon better understanding of their mechanistic basis, and refined mapping of their distribution by epidemiological and metagenomic studies.