Galaxy mergers are the process by which two or more galaxies merge gravitationally and ultimately merge. Galaxy mergers are important processes in galaxy evolution, structure formation, and starburst activity that fundamentally transform the morphology and stellar content of the participating galaxies.Galaxy mergers can be observed in various wavelengths, ranging from optical imaging of tidal features through infrared observations of dust-enshrouded starbursts to X-ray detection of interacting hot gas. Cosmological simulations reveal mergers are ubiquitous in hierarchical galaxy formation and assist in constructing larger galaxies from more modest progenitors over cosmic time.In short, galaxy mergers are central processes in the universe that determine galactic structure, induce star formation, and shape supermassive black hole growth. Through mergers, astronomers can learn about galaxy evolution, cosmic structure formation, and the stellar and gas life cycle in interacting systems.