Several position and consensus papers exist on the terminology used for probiotics, prebiotics, and synbiotics. These concern mostly viable. However, also inactive microbes and their metabolites have proven to be beneficial for health, and the evidence is rapidly increasing. Therefore we have assessed the current knowledge and science behind postbiotics, and we propose a definition for postbiotics to be as follows: compounds produced by microorganisms, released from food components or microbial constituents, including nonviable cells that, when administered in adequate amounts, promote health and well-being.