A molecular marker is a fragment or sequence of DNA that is associated with a certain location within the genome. The development of molecular marker technology has contributed significantly in crop improvement. In plant biotechnology, markers are used to reflect random sequences, genomic variants, or genes. Molecular markers are used majorly in the construction of DNA and genome maps. They also play a potential role in detecting crop tolerance to abiotic stresses, pathogen resistance, genetic diversity and agronomical characters. Marker-assisted selection (MAS) is a novel breeding tool used for more accurate and useful selections in breeding populations. There are several advantages of MAS including selection of genotypes at seedling stage, selecting traits with low heritability, and the ability to discriminate between homozygotes and heterozygotes. This book provides comprehensive insights into molecular marker technology and its applications in plant biotechnology. It will serve as a valuable source of reference for graduate and post graduate students.