General Language

An Etymological Dictionary of the Gaelic Language
CELT: Corpus of Electronic Texts
Dictionary of Medieval Latin from Celtic Sources
ASNC Spoken Word, University of Cambridge (Welsh, Irish, Continental Celtic)

Journals and Academic Programs/Affiliations

CELTICA – Journal of the School of Celtic Studies
Centre for Advanced Welsh and Celtic Studies, University of Wales
Dublin Institute for Advanced Studies
Scottish Place-Name Society

Old Irish

Old Irish Online: Series Introduction, University of Texas Austin
Old Irish Online: Grammar Introduction, University of Texas Austin
Old Irish Online: Base Form Dictionary, University of Texas Austin
In Dúil Bélrai: Old Irish Glossary, Sabhal Mór Ostaig (written in Modern Irish)
eDIL: Electronic Dictionary of the Irish Language

Irish Script on Screen
Locus: Irish Place-Name Project
Táin Bó Cúalgne, Vassar College
Scél Mucci Mic Dathó (The Story of Mac Dathó’s Pig), Vassar College

Middle Welsh

Dictionary of the Welsh Language, University of Wales
Reading Middle Welsh, MIT
Old and Middle Welsh, David Willis, University of Cambridge
Why Do I Need to Learn Middle Welsh?, Digital Medievalist Blog
Introduction to Welsh Orthography
Mutation of Initial Consonants in Middle Welsh, David Klausner
Checklist of Middle Welsh Particles