In view of the landmark attained with the first International Symposium on PQQ and Quinoproteins, it seemed a good opportunity to use the present contribution to evaluate the relevance of this topic for enzymology and related scientific disciplines. To this end, a short historical overview is given, the balance is drawn of the currently known quinoproteins, a comparision is made with well known cofactors, and finally some conclusions and prospects are presented. After a long and hidden past, the topic has reached the status of maturity and all requirements are met to become a fully-fledged part of enzymology.