Marine cold seeps are windows into different depth levels of the submerged geosphere. Subduction zones and organic-rich passive margins host most of the world’s cold seeps. The source of seep fluids ranges from 10s of meters (groundwater aquifers) to 10s of km (subducted oceanic plates) below the seafloor. Seeps transport dissolved and gaseous compounds upward and sustain oasis-type ecosystems at the seafloor. Hereby the single most important reaction is anoxic oxidation of methane (AOM) by Archaea. Subsequent reactions involve sulfur biogeochemistry and carbonate mineral precipitation generating an association of methane, metazoans, microbes, and minerals – a biogeochemical footprint. Currently 100s of cold seeps are known globally. Elucidating function, structure, and composition of the characteristic association are high-priority topics of cold seep research. Ancient seep sites are identified with increasing frequency as the libraries of biomarkers and fossilized microbial bodies grow aided by their fortuitous preservation as they become encased in carbonate precipitates. Seep footprints provide clues as to source depth, fluid-sediment/rock interaction during ascent, lifetime, and cyclicity of seepage events. The Gulf of Mexico, the Black Sea, and the Eastern Mediterranean Sea are sites of classic and ongoing seep studies.