NWU (National Writers Union): http://www.nwu.org/
OASIS (Organization for the Advancement of Structured Information Standards): http://www.oasis-open.org/
OCA (Open Content Alliance): http://www.opencontentalliance.org/
OCDE (Organisation de coopération et de développement économiques): http://www.oecd.org/
OCLC (Online Computer Library Center): http://www.oclc.org/
OCLC: WorldCat (catalogue): http://www.worldcat.org/
OCLC: WorldCat (infos): http://www.oclc.org/worldcat/
Odile Jacob (éditions): http://www.odilejacob.fr/
Odyssey Press: http://www.odysseypress.com/
OeBPS (open ebook publication structure): http://www.idpf.org/specs.htm