This thesis aims to investigate the use of prevention of mother-to-child transmission (PMTCT) of HIV services in rural Tanzania. Paper A, a systematic literature review of barriers and facilitating factors to the uptake of antiretroviral drugs for PMTCT in sub-Saharan Africa, identified many influencing factors at the level of individuals, their communities and health systems. Paper B discusses the challenges, including lack of unique identification numbers, associated with using routine clinic data for monitoring PMTCT programmes in Africa. Papers C and D use clinic data linked to community HIV cohort data to describe community-level access to PMTCT services among HIVpositive pregnant women. Paper C documented low, but increasing, coverage with PMTCT services in 2005-2012, with weaknesses throughout the PMTCT service continuum. Paper D identified women from remote areas, younger women, and unmarried women as less likely to access PMTCT services. Voluntary counselling and HIV testing before pregnancy, longer duration of HIV-infection, and more recent pregnancies were associated with improved PMTCT service use. Paper E critiques the use of a vignette within a qualitative investigation of barriers to PMTCT service uptake, suggesting that vignettes can be used successfully in rural Africa to draw out barriers to PMTCT service use. The qualitative analysis for paper F revealed a pivotal role for patient-provider interactions in PMTCT service use, through decision-making processes, trust, and features of care. The collective findings highlight the considerable barriers to uptake of PMTCT services that must be tackled in order to successfully eliminate new paediatric HIV infections. Potential positive impacts of ‘Option B+’ (initiating all HIV-positive pregnant women onto life-long antiretroviral therapy) may be limited by these barriers. Addressing health systems issues, particularly stock-outs of HIV test kits, drugs and delivery materials, and improving patient-provider relationships, may have the greatest immediate impact on PMTCT service use in this setting.