This is a protocol for a Cochrane Review (Intervention). The objectives are as follows: To determine the effects of conjugate Hib vaccine in preventing Hib disease or death in children under five years of age. To determine any variation in vaccine effectiveness with type of vaccine; number of doses; age at first dose; known HIV infection; or in high-income and low-income countries. To determine any clinically relevant mild, moderate or serious adverse outcomes. To identify costs associated with the vaccination, adverse events and illnesses in vaccinated and unvaccinated children.