Linkage disequilibrium (LD) refers to the nonrandom association of alleles at different loci, which is a sensitive indicator of population genetic forces. Evolutionary biologists and human geneticists are increasingly using LD to understand past evolutionary and demographic events, map genes associated with quantitative traits and inherited diseases, and understand the joint evolution of linked genes. LD is more extensively used in human studies than in non-human studies, but this is changing with technological advances that enable large-scale genomic studies in other species. LD is influenced by various factors, including natural selection, genetic drift, recombination, and mutation. The population genetics theory of LD provides insights into evolutionary history and is widely used for gene mapping in humans and other species. LD can be quantified using various statistics, and its patterns can reveal information about population history, breeding systems, and geographic subdivision. LD is also useful for detecting natural selection, inferring allele age, and understanding the impact of population subdivision and bottlenecks. The future of LD studies includes large-scale genome-wide association studies and the exploration of LD patterns in model organisms and other species.Linkage disequilibrium (LD) refers to the nonrandom association of alleles at different loci, which is a sensitive indicator of population genetic forces. Evolutionary biologists and human geneticists are increasingly using LD to understand past evolutionary and demographic events, map genes associated with quantitative traits and inherited diseases, and understand the joint evolution of linked genes. LD is more extensively used in human studies than in non-human studies, but this is changing with technological advances that enable large-scale genomic studies in other species. LD is influenced by various factors, including natural selection, genetic drift, recombination, and mutation. The population genetics theory of LD provides insights into evolutionary history and is widely used for gene mapping in humans and other species. LD can be quantified using various statistics, and its patterns can reveal information about population history, breeding systems, and geographic subdivision. LD is also useful for detecting natural selection, inferring allele age, and understanding the impact of population subdivision and bottlenecks. The future of LD studies includes large-scale genome-wide association studies and the exploration of LD patterns in model organisms and other species.