This book is part of the study of the determinants of non-use of full immunization among children aged 12 to 23 months in the Republic of Congo. Its main objective was to determine the factors that explain non-use of full immunization. It was theoretically based on economic, geographical, demographic and socio-cultural approaches. Analyses were based on data from the MCS 2015 survey collected on a target population of 1,708 children aged 12 to 23 months. The descriptive analysis made it possible to assess the prevalence of non-use of full vaccination for children aged 12 to 23 months, which was found to be at a rate of 68.3%. The results showed that the factors favoring non-use of full immunization among children aged 12 to 23 months were department, religion of the head of household, ethnicity of the head of household, mother's level of education, and mother's health culture, as well as other factors. The multivariate logistic regression analyses carried out confirm the purported association between department and non-use of full vaccination in general.