Tomato is a major vegetable crop valued by both consumers and the processing industry, with strong demand for traits such as high yield, improved quality, and resistance to pathogens, physiological disorders, and environmental stresses. Modern tomato cultivars have been developed through targeted introgression to incorporate desirable traits, resulting in high-yielding, disease-resistant varieties that also meet consumer preferences for superior quality and nutritional content. Research efforts have increasingly focused on identifying genes and quantitative trait loci (QTLs) associated with key quality attributes such as soluble sugars, total soluble solids, titratable acidity, pH, β-carotene, and lycopene. These components are critical indicators of table and processing quality, as well as potential health benefits due to their antioxidant properties. Despite this progress, the identification and functional characterization of useful QTLs for these traits from intraspecific crosses remain limited. This chapter aims to investigate the genetic mechanisms underlying fruit quality in a tomato population derived from an intraspecific cross, with the goal of supporting breeding efforts to enhance fruit quality and identify specific QTLs associated with key quality attributes. Understanding the genetics of quantitative traits is essential in plant biotechnology, as many agronomically and commercially important traits exhibit quantitative inheritance. QTLs are genomic regions associated with the variation of quantitative traits and may consist of individual genes or clusters of functionally related genes that collectively influence trait expression. QTL mapping is a widely used approach to locate these regions and can be applied to diverse types of mapping populations, including F2 populations, double haploids, backcross populations, and recombinant inbred lines. This chapter focuses on the application of QTL mapping and genome-wide selection in tomato, providing insights that will aid researchers in identifying current research gaps and deepening their understanding of fruit quality trait improvement in tomato breeding programs.