Editing Encyclopaedia of Chess Openings (section)

{{Short description|Reference work on chess openings}}
{{Italic title}}
[[File:Encyclopaedia of Chess Openings (volume E; 1978 edition).jpg|right|thumb|First edition of ''ECO'' volume E. The title is given in eight languages. In the center are the two openings included in the volume: 1.d4 Nf6 2.c4 e6; and  1.d4 Nf6 2.c4 g6 without (symbol ┘) an early ...d7–d5.]]

The '''''Encyclopaedia of Chess Openings''''' ('''''ECO''''') is a reference work describing the state of [[Chess theory#Opening theory|opening theory]] in [[chess]], originally published in five volumes from 1974 to 1979 by the [[Socialist Federal Republic of Yugoslavia|Yugoslavian]] company Šahovski Informator ([[Chess Informant]]). It is currently undergoing its fifth edition. ''ECO'' may also refer to the opening classification system used by the encyclopedia.
{{AN chess|pos=toc}}