Estimating the costs of interventions to increase childhood immunization coverage in low- and middle-income countries (LMICs) is essential for evidence-based policymaking. However, few studies focus on the costs of reaching zero-dose (ZD) children, and many lack standardized methodologies. This review published in Vaccines analyzes costing studies of interventions targeting ZD children in LMICs, revealing significant variation in intervention costs—from $0.08 per additional dose for SMS reminders in Kenya to $67 per dose for cash transfers in Nicaragua. Notably, only three of the 11 included studies provided detailed descriptions of their costing methods, making comparisons challenging. The findings highlight the need for standardized costing methodologies to enhance comparability across studies. Establishing research principles for ZD intervention costing could strengthen the evidence base, making it easier for policymakers to design effective, scalable programs and achieve global immunization equity.