OBJECTIVES: This first-ever country-level study assesses the implementation of the Helping Babies Breathe (HBB) program in 15 of Tanzania's mainland regions by measuring coverage, adoption and retention of provider skills, acceptability among providers, and barriers and challenges to at-scale implementation. METHODS: Longitudinal facility-level follow-up visits assessed provider resuscitation knowledge and skills in using objective structured clinical examinations and readiness of facilities to resuscitate newborns, in terms of birth attendants trained and essential equipment available and functional. Focus group discussions were held with providers to determine the acceptability, challenges, and barriers to implementation of the HBB program. RESULTS: Immediately after HBB training, 87.1% of providers passed the objective structured clinical examination. This number dropped to 79.4% at 4 to 6 weeks and 55.8% at 4 to 6 months (P < .001). Noting this fall-off in skills, the program implemented structured on-thejob training and supportive supervisory visits, which were associated with an improvement in skill retention. At long-term follow-up, >90% of facilities had bag-mask devices available to all beds in the labor and delivery ward, and 96% were functional. Overall, providers were highly satisfied with the HBB program but thought that the 1-day training used in Tanzania was too short, so they would welcome additional training and follow-up visits to reinforce skills. CONCLUSIONS: The HBB program in Tanzania has gained acceptability and shown success in equipping providers with neonatal resuscitation knowledge, skills, and supplies. However, assessing the program's impact on neonatal mortality has proven challenging.