Encyclopaedia of Chess Openings
CLASSIFICATION SYSTEM FOR THE OPENING MOVES IN A GAME OF CHESS
Encyclopedia of Chess Openings; ECO code; ECO codes; Encyclopaedia of chess openings; Opening Encyclopedia; Encyclopedia of chess openings; ECO (chess)
The Encyclopaedia of Chess Openings () is a reference work describing the state of opening theory in chess, originally published in five volumes from 1974 to 1979 by the Serbian company Šahovski Informator (Chess Informant). It is currently undergoing its fifth edition.