Loss and Damage (L&D), recognized as the third pillar of climate action, still lacks a standardized assessment methodology, posing a major challenge for vulnerable developing countries. This study identifies the most effective approaches for assessing L&D through a Systematic Literature Review (SLR). Following the PRISMA guidelines, a systematic search was conducted in the Scopus, PubMed, and Google Scholar databases for articles published between 2014 and 2024. After a comprehensive screening and quality appraisal process, 29 studies were selected for analysis. The findings reveal that no single methodology is dominant. Instead, mixed-methods approaches have become the most holistic and widely used, integrating the strengths of quantitative analysis (e.g., economic valuation, GIS modelling) with the depth of qualitative insights (e.g., interviews) to better capture Non-Economic Losses and Damages (NELD). The review also highlights a strong research bias toward extreme weather events compared to slow-onset processes, along with persistent challenges in NELD measurement, scientific attribution, and data standardization. In conclusion, the most effective approach to assessing L&D is one that is integrative, context-specific, and focused on human well-being. Future research should prioritize the development of participatory NELD methodologies and address data gaps to support more equitable and evidence-based climate policies.