Metaproteomics is an increasingly popular methodology that provides information regarding the metabolic functions of specific microbial taxa and can be used to assess environmental stressors and change and has potential for contributing to ocean ecology and biogeochemical studies. To enable future large-scale studies, a multi-laboratory intercomparison was conducted to assess comparability and reproducibility of taxonomic and functional results and their sensitivity to methodological variables. This ocean metaproteomic intercomparison consisted of two major activities: a laboratory component, where independent labs processed identical ocean samples simultaneously collected from the North Atlantic Ocean , and a subsequent informatic component.