The major challenges faced by plant breeders during the 21st century will be to increase crop production while enhancing the sustainability of agricultural practices and preserving the available biodiversity. A better knowledge of the genetic factors governing harvestable yield and its season-to-season variability will help breeders to more effectively devise strategies for improving yield potential and optimizing yield under a broad range of environmental conditions. Grain yield and the majority of the agronomic traits of interest are quantitatively inherited. The utilization of molecular markers and genomics platforms offers unprecedented opportunities to discover, select, and clone the quantitative trait loci (QTL) that govern such traits. The dissection of the genetic basis of quantitative traits into their single components provides direct access to valuable genetic diversity for the morpho-physiological features that regulate yield potential per se and the adaptative response to abiotic and biotic constraints. In this context, the main objectives of this Chapter are to provide the basic information on a number of topics important for an effective implementation and exploitation of molecular breeding. In view of the importance of quantitative traits in breeding activities, particular emphasis has been devoted to QTL mapping and the implementation of marker-assisted selection. Along with this information, some basic details have been provided concerning the methodologies, genetic resources and technological platforms utilized for dissecting the genetic basis of agronomic traits through molecular approaches.