Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection (LRTI) and hospitalization in infants and young children worldwide, with the highest disease burden occurring in otherwise healthy term infants during the first 6 months of life. The recent introduction of long-acting monoclonal antibodies and maternal RSV vaccination has fundamentally changed preventive strategies against severe RSV disease. Evidence from randomized clinical trials and large real-world studies consistently demonstrates that a single dose of Nirsevimab provides season-long protection against RSV-associated LRTI and reduces hospitalization rate across diverse infant populations, while maintaining an excellent safety profile. Emerging data also support its effectiveness in routine clinical practice, although important uncertainties remain regarding long-term epidemiological effects, viral evolution, resistance, comparative effectiveness with maternal immunization, and optimal implementation across different healthcare settings. Current evidence supports Nirsevimab as a major advance in infant RSV prevention. However, continued surveillance, comparative effectiveness studies, and equitable global implementation will be essential to maximize its long-term public health impact. This narrative review summarizes current evidence on Nirsevimab, with emphasis on its clinical efficacy, safety, real-world effectiveness, resistance, implementation challenges, cost-effectiveness, and its role alongside maternal RSV vaccination.