Molecular aging refers to changes at the molecular level that occur as organisms grow older, impacting cellular function, metabolism, and tissue integrity. Key mechanisms include telomere shortening, DNA damage accumulation, and oxidative stress, which contribute to cellular senescence and functional decline. Epigenetic modifications, such as changes in DNA methylation and histone acetylation, also influence gene expression patterns during aging. Age-related alterations in mitochondrial function and protein homeostasis (proteostasis) contribute to cellular aging and susceptibility to age-related diseases. Understanding molecular aging mechanisms informs strategies to promote healthy aging, develop therapies targeting age-related conditions, and extend healthspan in aging populations.