Lettuce (Lactuca sativa), an economically and nutritionally important leafy vegetable, has undergone extensive genetic improvement to enhance yield, disease resistance, abiotic stress tolerance, shelf life, and nutritional quality. The genetic resources of lettuce, including domesticated cultivars, landraces, and wild relatives, such as Lactuca serriola, Lactuca virosa, and Lactuca saligna, serve as invaluable reservoirs of genetic diversity. These resources provide critical alleles for improving agronomic traits, ensuring sustainable production, and enhancing climate resilience. Recent advancements in plant genomics, particularly next-generation sequencing (NGS), genome-wide association studies (GWAS), marker-assisted selection (MAS), and genomic selection (GS), have revolutionized lettuce breeding strategies by enabling precise trait mapping and selection. The advent of CRISPR-Cas9 genome editing has further accelerated the development of novel lettuce cultivars with improved resistance to pathogens, extended postharvest longevity, and enhanced phytochemical composition. Additionally, the integration of multi-omics approaches, including transcriptomics, proteomics, and metabolomics, has facilitated a deeper understanding of gene regulatory networks and metabolic pathways influencing key traits. Conservation and characterization of lettuce germplasm through advanced genomic tools are crucial for harnessing genetic diversity and mitigating the risks associated with genetic erosion. This review provides a comprehensive overview of lettuce genetic resources, their conservation strategies, and their utilization in modern breeding programs, emphasizing cutting-edge genomic innovations. Furthermore, it discusses current challenges, such as the limited genetic base in cultivated lettuce, the impact of climate change on genetic diversity, and the need for sustainable breeding approaches to develop climate-smart, nutritionally superior lettuce varieties.