|i.||Names in 'Mc' and 'Mac' are ordered as if spelled 'Mac' and grouped together before other headwords beginning with 'M'.|
|ii.||However, it should be noted that surnames began to be used only in the eleventh century. Before then 'A mac B' (distinguished by lower-case 'mac') meant that A was literally the son of B. Biographical entries from this period are grouped under Christian name: thus Áedán mac Gabráin appears under 'A', not 'Mac'.|
|iii.||For similar reasons early English (or 'Norman', though see the entry on this label) names are written with lower-case 'f' for 'fitz'. But these are nevertheless, following the usual convention, listed under 'F'.|
|iv.||Names beginning with 'de' are ordered according to the main part of the name, for example de Lacy under 'L', de Valera under 'V'.|
For the period up to 1169 personal names are given in the Irish form, with anglicized versions in brackets. Thereafter they are given in the anglicized form, with Gaelic versions, where necessary, in brackets. Those whose careers straddle that borderline have had to be allocated to one side or the other: thus 'Diarmait Mac Murchada (Dermot MacMurrough)', but 'Rory O'Connor (Ruaidrí Ua Conchobair)'.
Place names have been given in their contemporary form, with modern equivalents supplied where appropriate, for example 'King's Country (Offaly)'. Following a commonly adopted compromise, we refer to the city of Derry and the county of Londonderry.
The bibliographies attached to longer entries are necessarily selective. Preference has