Studies have shown that colonization of the nasopharynx by potential respiratory pathogens Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis is established early in childhood, although rates vary greatly according to locality, sampling frequency, individual and social factors. Factors influencing colonization and elimination are not as yet fully understood, but adhesion to mucosal receptors and immune responses are implicated in addition to bacterial properties and colonization resistance dynamics. Colonization in children and adults has been intensively studied in various localities. Potential pathogens are more likely to colonize the nasopharynx of children prone to recurrent otitis media, where impaired local immunity and repeated exposure to respiratory pathogens are additional risk factors. Adults with chronic respiratory tract disease also have higher carriage rates. The factors contributing to increased risk of carriage of potential respiratory pathogens, as well as to clinical infection and antimicrobial resistance, are summarized in this review.