State and urban immunization programs are responsible for the implementation of comprehensive programs to vaccinate populations within their geographic area. Given the variability in immunization coverage rates between geographic areas, the purpose of this two-phase study was to first identify the state and urban areas that achieved the highest increases in coverage, and then those with the highest sustained coverage, between two designated periods, and to interview key program staff members and their community counterparts to capture their perspectives on what factors may have contributed to increasing and sustaining high rates. In this article, we describe phase 1, in which we visited the seven sites that achieved the largest increases in coverage from 2001 to 2004. Results describe outcomes from the 71 semistructured key informant interviews with internal staff and external partners at the site's immunization programs. Interview transcripts were analyzed qualitatively, using a general inductive approach. Common challenges encountered among the seven sites included increasing reluctance among parents and overcoming barriers to accessing care. Common strategies to address these and other challenges included collecting and using data on immunization coverage, developing communication and education efforts, and continuously reaching out and collaborating with immunization partners. Lessons learned from these programs may help inform others who are working to improve childhood immunization delivery and coverage in their own programs.