| O Neill |
| S-00002700 | Anglo-Norman Ulster | ||
| Obertenghi |
| S-00000017 | Genealogie Medioevali di Sardegna | ||
| Oberto |
| S-00001004 | CEF - Structures Familiales en Lombardie, Émilie et Toscane | ||
| Obotrites |
| S-00000130 | GMG - Descendants of King Harold | ||
| O'Cahan |
| S-00001290 | TSG - Possible Medieval Origins of Budge Name | ||
| Occlestone |
| S-00001727 | TAN - Some Cheshire Deeds | ||
| O'Conor |
| S-00001231 | Ireland under the Normans, 1216-1333 | ||
| Oda |
| S-00000954 | ADB - Origines Maternelles de Bourgogne Otte-Guillaume | ||
| Odard |
| S-00002582 | CWX - Odard Vicecomes | ||
| S-00002712 | FND - Five Odards | ||
| S-00002430 | TAN - Some Extinct Cumberland Families | ||
| Odcombe |
| S-00002679 | TAN - Possible Samborne Ancestry | ||
| Odda |
| S-00002524 | ANS - Earls of Mercia and their Commended Men | ||
| S-00002523 | ANS - Political Style in Late Anglo-Saxon England | ||
| S-00002538 | ANS - Thegnly Piety and Ecclesiastical Patronage | ||
| Oddingeseles |
| S-00002648 | TAN - Clinton Famil | ||
| Odenkirchen |
| S-00001248 | PRS - Archiepiscopal Counts of Cologne | ||
| Odense |
| S-00002253 | ANS - Eleventh-Century Missions | ||
| Oderisius |
| S-00001966 | MPR - Eleventh-Century Noble Family from Central Italy | ||
| Odingselles |
| S-00001609 | TPG - Descent of Meignell and Clinton | ||
| Odo |
| S-00002157 | ANS - Bayeux Tapestry: Why Eustace,Odo and William? | ||
| S-00002119 | ANS - Byzantine Marginalia to the Norman Conquest | ||
| S-00002132 | ANS - Towards an Interpretation of the Bayeux Tapestry | ||
| S-00002449 | TAN - Origin of the Carews | ||
| Odrocia |
| S-00000947 | GAM - Descendientes del Conde Ero Fernández | ||
| Offa |
| S-00002454 | TAN - Pictures of English Dress | ||
| Ogard |
| S-00002591 | TGC - Sir Andrew Ogard, a 'Stranger Knight' | ||
| Ogilvy |
| S-00001319 | TSG - Henry Scrymgeour, 1506-1572 | ||
| S-00001331 | TSG - Murray of Cullow | ||
| S-00001337 | TSG - Ogilvy of Inverquharity | ||
| S-00001339 | TSG - Ogilvys of Clova | ||
| S-00001340 | TSG - Scrymgeour of Glaswell | ||
| S-00001312 | TSG - Sir John Ogilvy | ||
| Ogle |
| S-00001725 | TAN - Our Oldest Families | ||
| Ogmore Castle |
| S-00001405 | Ogmore Castle | ||
| Ogston |
| S-00001323 | TSG - Ogston of that Ilk | ||
| Oilly |
| S-00001660 | FND - Pedigree of the Earls of Warwick | ||
| Okeover |
| S-00001725 | TAN - Our Oldest Families | ||
| Oketon |
| S-00001619 | TPG - Charter of Robert de Neville | ||
| Old Langport |
| S-00001685 | TPG - Domestic Chronicle of Thomas Godfrey | ||
| Oldenburg |
| S-00000866 | GMG - Paternal Ancestry of Duke of Edinburgh | ||
| S-00000872 | GMG - Paternal Ancestry of Duke of Edinburgh (Letter from CFH Evans) | ||
| S-00001267 | Lines of Succession | ||
| S-00001178 | TSG - Informal Talk on Pedigrees and Ancestors | ||
| Oldham |
| S-00001964 | MPR - Chapter of Lincoln Cathedral 1300-1541 | ||
| Olifard |
| S-00002405 | TDT - Look at Early Murray Arms | ||
| S-00001306 | TSG - Condy/Condie Surname | ||
| Oliphant |
| S-00001306 | TSG - Condy/Condie Surname | ||
| S-00001291 | TSG - Sketch for an Elphinstone Genealogy (Pts 1, 2, 4, 5) | ||
| Oliver King |
| S-00001969 | MPR - Foppish Eleven of 1483 | ||
| Olivier |
| S-00001002 | LMA - Rayonnement de la 'Chanson de Roland' | ||
| Olympias |
| S-00000978 | TSH - Fifteenth-century Bagratids in Georgia | ||
| Ommatius |
| S-00000955 | FWG - Ruricius Ier, Évęque de Limoges | ||
| Oneal |
| S-00001693 | TPG - Exactions Incident to Tenures in Ireland | ||
| Oratio |
| S-00002208 | ANS - Oratio de Utensilibus ad Domum Regendam Pertinentibus | ||
| Orbec |
| S-00000267 | GMG - Généalogie des Seigneurs d'Orbec (Book Review) | ||
| Order of St John |
| S-00000793 | A Modern Crusade | ||
| Orderic |
| S-00001027 | TRH - First House of Bellęme | ||
| Orderic Vitalis |
| S-00002104 | ANS - Aimeri of Thouars and the Poitevin Connection | ||
| S-00002324 | ANS - Clio's Legal Cosmetics | ||
| S-00001539 | ANS - Feudal Society in Orderic Vitalis | ||
| S-00001580 | ANS - Gens Normannorum | ||
| S-00001576 | ANS - Introduction of Knight Service into England | ||
| S-00002570 | HSJ - King Stephen's Norman Itinerary | ||
| S-00002313 | HSJ - Women in Orderic Vitalis | ||
| Ordońo |
| S-00000944 | AEM - Conde Fernando Peláez, un Rebelde Leonés | ||
| S-00000945 | ARM - Linaje Castellano de Castro en el Siglo XII | ||
| S-00000947 | GAM - Descendientes del Conde Ero Fernández | ||
| Oriel |
| S-00000018 | TGC - Eve of Leinster | ||
| Oristano |
| S-00002666 | ASS - Serie Cronologica dei Giudici Sardi | ||
| Orkney |
| S-00002253 | ANS - Eleventh-Century Missions | ||
| S-00000818 | Earl and Mormaer | ||
| S-00000188 | GMG - Ancestry of William I | ||
| S-00000104 | GMG - British Families in Norway (Pt 1) | ||
| S-00000148 | Rossiana | ||
| S-00000075 | TGC - Marjory Sutherland, Countess of Caithness | ||
| S-00001151 | TSG - Arms of Maxwell of Calderwood | ||
| S-00001315 | TSG - McDowall (Letter from NSF Cram-Sinclair) | ||
| S-00001124 | TSG - Old Norse Nicknames in Scotland | ||
| S-00001189 | TSG - Research of the Old Royal House of Moray | ||
| S-00001187 | TSG - Scottish Arms in the Bellenville Roll | ||
| S-00001299 | TSG - Some Notes on Early Tullochs | ||
| orle |
| S-00002489 | TDT - Orle or 'Scutcheon Voided | ||
| Orléans |
| S-00001888 | MPR - Deputies at the French Estates General | ||
| S-00000245 | PEG - Onomastique et Parenté - Comtes de Gâtinais | ||
| S-00000246 | PEG - Onomastique et Parenté - Vicomtes de Châteaudun | ||
| Orm |
| S-00002538 | ANS - Thegnly Piety and Ecclesiastical Patronage | ||
| S-00002702 | FND - Gospatric, Lord of Workington | ||
| S-00002644 | TAN - Curwens of Workington | ||
| Ormesby |
| S-00002824 | NEH - Early Settlers of Hampton | ||
| S-00002827 | NEH - English Background of Early Settlers of Hampton | ||
| Ormond |
| S-00000771 | GMG - Ancestry of Queen Anne Boleyn | ||
| S-00001693 | TPG - Exactions Incident to Tenures in Ireland | ||
| Ormonde |
| S-00001359 | GMG - Descent from the Saints | ||
| S-00002830 | TGB - Ormonde Attainders | ||
| S-00001384 | TPG - Inedited Additions to the Pedigree of Babington | ||
| Ormsby |
| S-00002618 | TAN - Massingberds of Sutterton, Gunby and Ormsby | ||
| Oronsay |
| S-00002350 | TSG - Have the MacFies Got it Wrong? | ||
| O'Rourke |
| S-00002632 | TAN - Account of the Sheridan Family | ||
| Orrů |
| S-00000017 | Genealogie Medioevali di Sardegna | ||
| Orseolo |
| S-00000995 | SEZ - Géza Nagyfejedelem és Családja | ||
| S-00000988 | UZU - Byzantinsche Prinzessinnen in Ungarn | ||
| Orsini |
| S-00000594 | Despotate of Epiros 1267-1479 | ||
| Orthe |
| S-00001646 | GMG - Henry V's Illegitimate Niece? | ||
| Osbaldeston |
| S-00002365 | TGB - Dugdale's Visitation of Yorkshire | ||
| Osbern |
| S-00002102 | ANS - Norman Settlement of Herefordshire | ||
| S-00002433 | TAN - Genealogy of the Giffards | ||
| Osorio |
| S-00000945 | ARM - Linaje Castellano de Castro en el Siglo XII | ||
| S-00002675 | GJB - Dońa Leonor Alvarez de Toledo | ||
| S-00000147 | Historia Genealógica Argentina | ||
| Osraige |
| S-00000018 | TGC - Eve of Leinster | ||
| Osric |
| S-00002703 | FND - Anglo-Saxon Aristocracy | ||
| S-00002716 | NQU - Anglo-Saxon Chronicle for 755 | ||
| Osthryth |
| S-00002780 | HSJ - Monk-Kings | ||
| Ostrogoths |
| S-00001371 | Italy and her Invaders | ||
| Oswald |
| S-00002780 | HSJ - Monk-Kings | ||
| Oswulf |
| S-00002783 | HSJ - Pre-Conquest Christ Church | ||
| Othon |
| S-00000986 | ADB - Propos de la 'Guerre de Bourgogne' | ||
| S-00001000 | JDS - Mathilde, Reine de France Inconnue | ||
| S-00002573 | Maison de Lorraine | ||
| Otte-Guillaume |
| S-00000986 | ADB - Propos de la 'Guerre de Bourgogne' | ||
| Otto |
| S-00000954 | ADB - Origines Maternelles de Bourgogne Otte-Guillaume | ||
| S-00001013 | DAM - Hermann von Schwaben als Prüfstein | ||
| S-00001011 | VSN - Südtiroler als Wähler des Römisch-Deutschen Königs | ||
| S-00001015 | ZSR - Genealogie der Konradiner | ||
| Otto I |
| S-00001775 | Alterere Genealogie der Andescher | ||
| S-00002509 | Aus dem Blute Widukinds | ||
| Otton |
| S-00002507 | Wicman II, Comte du Hamaland | ||
| Ottone |
| S-00002724 | Origini di una Famiglia Nobile Pisana | ||
| Ottonian |
| S-00001912 | MPR - Patterns of Women's Names in Royal Lineages | ||
| Ottreply |
| S-00001689 | TPG - Some Account of the Manor of Apuldrefield | ||
| Oudenaarde |
| S-00002427 | Flemish Nobility before 1300 | ||
| S-00000725 | Vlaamse Adel voor 1300 | ||
| Outremer |
| S-00002665 | Feudal Nobility of the Crusader Kingdom of Jerusalem | ||
| S-00001236 | PRS - Prosopographical Research on the Crusader States | ||
| Over, Cambridgeshire |
| S-00002160 | ANS - Life-Grants of Land and the Development of Inheritance | ||
| Owain |
| S-00002500 | BBC - Achau Brenhinoedd a Thywysogion Cymru | ||
| S-00002555 | HSJ - Ynfydion of Gruffudd ap Rhys Reconsidered | ||
| Owen |
| S-00002658 | AAS - Decline of the Tudors of Penmynydd | ||
| S-00000870 | GMG - Sir Nicholas de Loveyne | ||
| Oxford |
| S-00000129 | GMG - Calendar of Close Rolls, Henry V (Book Review) | ||
| S-00000225 | GMG - Calendar of Fine Rolls (2) (Book Review) | ||
| S-00000185 | GMG - Calendar of Fine Rolls (Book Review) | ||
| S-00000214 | GMG - Calendar of Inquisitions Post Mortem (Book Review) | ||
| S-00000192 | GMG - Close Rolls of Henry III (2) (Book Review) | ||
| S-00000269 | GMG - Complete Peerage (Book Review) | ||
| S-00000198 | GMG - Coronation Claims | ||
| S-00000190 | GMG - Curia Regis Roll of Richard I and John (Book Review) | ||
| S-00000292 | GMG - Curia Regis Rolls of Henry III (2) (Book Review) | ||
| S-00000304 | GMG - Great Officers of State | ||
| S-00000163 | GMG - Great Roll of the Pipe (Book Review) | ||
| S-00000294 | GMG - Harrold Priory (Book Review) | ||
| S-00000265 | GMG - Notes on Anglo-Norman Genealogy | ||
| S-00000870 | GMG - Sir Nicholas de Loveyne | ||
| S-00000179 | GMG - Some Aspects of Heraldry | ||
| S-00000865 | GMG - William de Lichfeld | ||
| S-00002003 | MPR - Prosopography of Irish Scholars | ||
| Oxford Archdeaconry |
| S-00002050 | OFH - Genealogical Sources at Lincolnshire Archives Office | ||
| Oxfordshire |
| S-00000197 | GMG - Quatremains of Oxfordshire (Book Review) | ||
| S-00000126 | GMG - South Newington and The Giffards | ||
| S-00002048 | OFH - Bibliography for Oxon, Berks and Bucks | ||
| S-00002050 | OFH - Genealogical Sources at Lincolnshire Archives Office | ||
| S-00001682 | TPG - Ancient Deeds, Bucks and Oxon | ||
| S-00001379 | TPG - Pedigree of the Family of Hord | ||
| G-00000233 | Oxfordshire Family Historian | ||
| Oxon |
| S-00002048 | OFH - Bibliography for Oxon, Berks and Bucks | ||
| S-00002050 | OFH - Genealogical Sources at Lincolnshire Archives Office | ||
| Oxton |
| S-00000053 | TGC - Trowbridge Ancestry | ||
| Oystermouth Castle |
| S-00001424 | Oystermouth Castle | ||