Authors
- Patrick O'Brian 3
- Edna O'Brien 2
- M.J. O'Carroll 1
- Eileen O'Casey 1
- Daniel O'Connor 1
- Flannery O'Connor 1
- Frank O'Connor 1
- Raymond J. O'Connor 1
- Terry O'Connor 1
- Roy O'Dell 3
- Elliott O'Donnell 1
- Mabel O'Donnell 4
- Kevin O'Donoghue 1
- Eileen O'Faolain 1
- Mervyn O'Gorman 1
- K.T. O'Grady 1
- Mark O'Hanlon 1
- Redmond O'Hanlon 1
- C.W. O'Hara 2
- Kane O'Hara 1
- Vincent P. O'Hara 1
- Colette O'Hare 2
- Cleophas C. O'Harra 1
- James O'Keefe 1
- Adelaide O'Keeffe 2
- Eamonn O'Keeffe 1
- Paul O'Keeffe 2
- Michael O'Leary 4
- Brian D. O'Neill 1
- John P. O'Neill 1
- Moira O'Neill 1
- Robert O'Neill 1
- Tom O'Reilly 1
- Joseph O'Rourke 1
- Tyrone O'Sullivan 1
- Peter Oakes 1
- E.R. Oakley 1
- Graham Oakley 2
- Michael Oakley 1
- Mike Oakley 1
- J.A. Oates 1
- Jonathan Oates 1
- Ralf Obergfell 1
- Ulrich Oberprieler 1
- Martin Odersky 1
- Waclaw Odyniec 1
- Richard Offner 1
- Christopher Ogborne 1
- Angela Ogden 2
- J. Douglas Ogilby 1
- Malcolm A. Ogilvie 1
- Will H. Ogilvie 4
- David Ogilvy 1
- James S. Ogilvy 1
- Arthur Oglesby 1
- Bob Ogley 4
- Hideaki Ohba 1
- Jane Ohlmeyer 1
- Thomas Okey 1
- Bernt Oksendal 1
- Charles S. Olcott 1
- Veena Taiwar Oldenburg 1
- Jenny Oldfield 1
- Paul Oldfield 1
- Katharine Oldmeadow 5
- Achille Bonito Oliva 1
- W.H.T. Olive 1
- David Oliver 3
- Earl D. Oliver 1
- George Oliver 1
- H.J. Oliver 1
- Jennie A. Oliver 1
- Jocelyn Oliver 1
- Michael Oliver 2
- Thomas Oliver 1
- Torfrida Oliver 1
- Henry Olivier 1
- Jean Moulin Ollagnier 1
- Don Olney 1
- John Andreas Olsen 1
- Klaus Malling Olsen 2
- Lars-Henrik Olsen 1
- Penny Olsen 1
- Gary D. Olson 1
- James S. Olson 1
- Lynne Olson 1
- Storrs L. Olson 1
- Urban Olsson 1
- Sir Charles Oman 1
- F.D. Ommanney 1
- Willem Oosthoek 2
- Iona Opie 11
- Peter Opie 7
- Hiawyn Oram 1
- Vincent Orange 1
- Laurence F. Orbach 1
- Arthur W.J.G. Ord-Hume 2
- T. Fairman Ordish 1
- Doris Orgel 1
- Iris Origo 1