Lettuce, a widely cultivated annual crop belonging to the Asteraceae family, is extensively utilized in salads, sandwiches, and various other culinary applications. It exhibits a diverse array of types and forms, characterized by a range of colors, textures, margins, and leaf surfaces. Although over a hundred species of Lactuca have been documented, only a limited number can be successfully hybridized through traditional breeding methods. Conventional breeding practices integrate genotypes from various genetic sources to increase genetic variation and select for desirable traits, including high yield, early maturity, improved quality, pest resistance, and environmental stress tolerance. While innovative biotechnological approaches are gaining traction, traditional agricultural practices remain vital for enhancing lettuce genotypes with preferred characteristics. Therefore, underlying footprint cohorts and their integration to assisted breeding are crucial to understand to realize breeding vision. Current technologies offer solutions to these challenges to several extent; however, further advancements are necessary to satisfy the increasing demand for superior product appearance, quality, biosafety, and reduced economic and environmental costs. This chapter explores the diversity of lettuce germplasm and its applications in conventional breeding by leveraging genome-wide association studies and quantitative trait locus (QTL) mapping to facilitate lettuce improvement through advanced tools and technologies-assisted breeding.