This chapter considers the evolution of the vaccination system and its records, as the former very much influenced the latter, setting limits on the use of the records in research. It illustrates the potential of this valuable source to our understanding of the decline in infant mortality by investigating infant mortality amongst the population of Higham Ferrers registration sub-district, a shoe-making district in the county of Northamptonshire in the final decades of the nineteenth century. Originally variolation and then vaccination were promoted chiefly through charitable sources such as the first National Vaccine Establishment founded but, following the first Vaccination Act, vaccination became the remit of the Boards of Guardians responsible for the administration of the Poor Law. Alongside the vaccination birth registers, registers of infant deaths (IDRs) were also compiled on a monthly basis, from information provided by the Registrars.