Immunization has proven to be one of the most cost-effective public health interventions to date. Not only has immunization saved millions of lives, but it has also protected children from severe illness and life-changing disability. Measles, which had once been a significant childhood killer, is now targeted for elimination. Worldwide measles vaccination has led to a 71% decrease in measles-related deaths and an 88% reduction the World Health Organization African Region (WHO-AFRO) alone. In the Democratic Republic of Congo (DRC), measles immunization has had a profound effect on reducing childhood mortality; however, beginning in 2010 large-scale measles outbreaks threatened past successes. Suspected case counts increased dramatically. This was mainly attributed to a weak routine immunization system and missed supplementary immunization activities. This dissertation aims to inform the improvement and further development of the immunization program in DRC by assessing measles immunization effects, vaccine effectiveness, and compares the cost-effectiveness of different immunization strategies. Chapter 1 is a brief introduction to measles immunization worldwide and in DRC. Chapter 2 is based on measles surveillance data from the Integrated Disease Surveillance and Response (IDSR) and demonstrated that measles immunization, in particular mass campaigns are extremely effective in DRC. Chapter 3 utilized case-based surveillance data with laboratory confirmation to estimate measles vaccine effectiveness. Finally, chapter 4 further solidifies the importance of mass campaigns in DRC until routine immunization is further strengthened through a cost-effectiveness analysis of three different vaccination strategies.