Heterosis, commonly known as hybrid vigor or outbreeding enhancement, refers to the phenomenon where hybrid offspring exhibit superior biological qualities compared to their parents. This enhancement can manifest in various traits, including increased size, growth rate, fertility, and yield. The concept of heterosis has been extensively studied and utilized in agriculture to improve crop and livestock performance. The underlying mechanisms of heterosis are complex and involve both genetic and epigenetic factors. Two primary genetic hypotheses have been proposed to explain heterosis: the dominance hypothesis and the overdominance hypothesis. The dominance hypothesis suggests that hybrid vigor arises when deleterious recessive alleles from one parent are masked by dominant alleles from the other parent, leading to improved performance. In contrast, the overdominance hypothesis posits that certain allelic combinations in a heterozygous state confer superior traits compared to either homozygous condition. Epigenetic factors, such as DNA methylation and histone modification, also play a role in heterosis by influencing gene expression without altering the underlying DNA sequence. These epigenetic modifications can result in the activation or repression of specific genes, contributing to the enhanced traits observed in hybrids. In plants, heterosis has been widely exploited to develop high-yielding hybrid varieties. For instance, hybrid maize (corn) exhibits significant heterosis, leading to increased grain production and resilience to environmental stresses. Similarly, hybrid rice varieties have been developed to enhance yield and disease resistance, contributing to food security in many regions. In animals, heterosis is observed in various species, including livestock and poultry. Crossbreeding in cattle, for example, can result in offspring with improved growth rates, fertility, and adaptability to different environments. In poultry, hybrid vigor is utilized to produce broiler chickens with rapid growth and high feed efficiency. However, not all hybridizations result in heterosis. In some cases, crossing genetically distant individuals can lead to outbreeding depression, where the offspring exhibit reduced fitness. This reduction can occur due to the disruption of coadapted gene complexes or the introduction of incompatible genetic material. Therefore, careful selection of parent lines is crucial to achieve the desired heterotic effects. The study of heterosis continues to be a dynamic field, with ongoing research aimed at unraveling the precise genetic and molecular mechanisms underlying this phenomenon. Advancements in genomic technologies and bioinformatics are facilitating deeper insights into the complex interactions that contribute to hybrid vigor. Understanding these mechanisms holds the potential to further enhance agricultural productivity and address challenges related to food security and sustainable farming practices.