**1. Introduction**

Molecular breeding (MB) may be defined in a broad-sense as the use of genetic manipula‐ tion performed at DNA molecular levels to improve characters of interest in plants and ani‐ mals, including genetic engineering or gene manipulation, molecular marker-assisted selection, genomic selection, etc. More often, however, molecular breeding implies molecu‐ lar marker-assisted breeding (MAB) and is defined as the application of molecular biotech‐ nologies, specifically molecular markers, in combination with linkage maps and genomics, to alter and improve plant or animal traits on the basis of genotypic assays. This term is used to describe several modern breeding strategies, including marker-assisted selection (MAS), marker-assisted backcrossing (MABC), marker-assisted recurrent selection (MARS), and genome-wide selection (GWS) or genomic selection (GS) (Ribaut et al., 2010). In this ar‐ ticle, we will address general principles and methodologies of marker-assisted breeding in plants and discuss some issues related to the procedures and applications of this methodolo‐ gy in practical breeding, including marker-assisted selection, marker-based backcrossing, marker-based pyramiding of multiple genes, etc., beginning with a brief introduction to mo‐ lecular markers as a powerful tool for plant breeding.
