Conjugate vaccines--bacterial polysaccharides conjugated to proteins to improve their immunizing properties--have been a success story since their introduction less than 20 years ago. The Haemophilus influenzae type b conjugate vaccine has nearly eliminated invasive Haemophilus influenzae type b disease in large parts of the world. The key reasons for its success are its ability to induce immunologic memory and reduce asymptomatic carriage, hence the spread of infection. The first pneumococcal conjugate vaccine was licensed in 2000 and is already in wide demand in the USA. The first meningococcal conjugate vaccine was introduced in a nationwide program in the UK in 1999. Current discussion focuses on the efficacy of the conjugate vaccines for different end-points and the cost-effectiveness of their use globally.