Here are some book recommendations and links to websites, apps and audio and video resources. Our Youtube channel also has a collection of useful videos in our language playlist.

Gaeilge (Irish)

Learning Irish by Michael Ó Siadhail
Teach Yourself Irish by Diarmuid Ó Se and Joseph Sheils
Colloquial Irish: The Complete Course for Beginners by Thomas Ihde
Basic Irish: A Grammar and Workbook by Nancy Stenson
Intermediate Irish: A Grammar and Workbook by Nancy Stenson
Foclóir Gaeilge-Béarla by Niall Ó Dónaill
Modern Irish: Grammatical Structure and Dialectal Variation by Michael Ó Siadhail
Irish Grammar: A Basic Handbook by Noel McGonagle
Who Needs Irish?: Reflections on the Importance of the Irish Language Today by Ciarán Mac Murchaidh
Progress in Irish: A Graded Course for Beginners and Revision by Máiréad Ní Ghráda
Complete Irish with Two Audio CDs: A Teach Yourself Guide by Diarmuid Ó Sé
Teach Yourself Irish Grammar by Eamonn Ó Dónaill
Buntús Cainte: A First Step in Spoken Irish by Tomas O’Domhnallain
Collins Irish Dictionary by Séamus Mac Mathúna
Usborne Everyday Words: Irish Flashcards by Felicity Brooks and Jo Litchfield
Everyday Words in Irish by Jo Litchfield

Buntús Cainte Ceim a hAon: A First Step in Spoken Irish by Tomas O Domhnallain (also available for iPhone/iPad/iPod)
Singing in Irish Gaelic by Mary McLaughlin
Spoken World: Irish by Living Language
Rosetta Stone: Irish
How to Pronounce Irish for Beginners by Gearóid

Online Dictionaries
Irish Dictionary Online

A Beginners Guide to Irish Pronunciation
Irish Language Information and Resources
Irish Language: Irish language schools, dictionary, words and other resources about Irish
Language @ Irish Culture and Customs
Irish Lesson with Dennis Doyle (audio pronunciation guide)
BBC — Cluichí Teanga
An Malamor

Courses and Apps
Duolingo (free/online/app available)
Conradh na Gaeilge Shasana Nua: The Gaelic League of New England
The Philo-Celtic Society (free/online)
RTÉ — Easy Irish (free/online)
Talk Irish (subscription needed/online)
Irish Gaelic by Nemo (free app)
Learn Irish Premium (app)
AbairLeatOIDE by Coláiste Lurgan (free app)
TG Lurgan by Coláiste Lurgan (free app)
Cúla Caint (free app)

An Droichead
Digital Dialects — Games for learning Irish

TG4 (Irish language programming)
RTÉ (Ireland’s national television and radio)
Raidió na Life (Irish language radio)
Raidió na Gaeltachta (Irish language radio from RTÉ)
TG Lurgan (Irish language Youtube)

Gàidhlig (Scots Gaelic)

Colloquial Scottish Gaelic: The Complete Course for Beginners by Katherine M. Spadaro
Teach Yourself Gaelic by Roderick MacKinnon
Gaelic-English Dictionary by Colin Marks
Faclair na Pàrlamaid, produced by the Scottish Parliament
Sabhal Mòr Ostaig’s An Stòr-data Briathrachais Gàidhlig
Complete Gaelic with Two Audio CDs: A Teach Yourself Guide
by Boyd Robertson and Iain Taylor
Scots Gaelic: An Introduction to the Basics by George McLennan
The Practical Guide to Gaelic Pronunciation by Michael Bauer
Speaking Our Language by Richard Cox

Online Dictionaries
MacBain’s Dictionary(useful for older Gaelic orthography)
Dwelly’s Classic Scottish Dictionary (useful for older Gaelic orthography)
Am Faclair Beag (modern Gaelic)
An Seotal: A Gaelic Terminology Database

Fòram na Gàidhlig
Learn Gaelic
Ùlpan — Gaelic for adults
Ceantar — Gaelic Languages Info
Save Gaelic

Courses and Apps
Classes and Distance Learning (via An Comunn Gàidhealach Ameireaganach)
The Access Course (via Sabhal Mòr Ostaig)
Cille Conval Gaelic Partnership — Gaelic Lessons
Bruidhinn ar Cànan | Speaking Our Language (lessons)
Comhairle na Gàidhlig: The Gaelic Council of Nova Scotia
Memrise Scottish Gaelic Courses (free online/app available)
BBC — Alba — Beag Air Bheag (free online)
Stòras na Gàidhlig
Fuaimean na Gàidhlig
One Minute Gaelic
Taic (free online)
Scottish Gaelic ABC by Cànan Ltd (free app)
Goireasan Gàidhlig: uTalk Scottish Gaelic  (app)
Bòrd na Gàidhlig (free app)
Scottish Verbs LearnBots (free app)
Guthan Beaga: Small Voices (free app)
Faclair na Sgoile (free dictionary app)
Play and Learn Gaelic (app)

Tetris in Gaelic
An Crochadair — Hangman in Gaelic

BBC — Radio nan Gàidheal
BBC — An Litir Bheag
BBC — Litir do Luchd-ionnsachaidh
BBC — Dealas (intermediate interactive resources)
Speaking Our Language (videos)
Speaking Our Language (downloadable worksheets)

Gaelg (Manx)

Focklioar Giare: Gaelg – Baarle by Illiam Wood
Practical Manx by Jennifer Kewley Draskau

Online Dictionaries
Online Manx Dictionaries

Failt erriu as bannaghtyn dys Ynsee Gaelg – Learn Manx
Manx Gaelic: Chengey-ny-Mayrey Vannin
Gaelg er yn Eggey
Gaelg Lessoonyn
Manx/Toshiaght — Free language book online

Courses and Apps
Learn Manx — Ynsee Gaelg (free app)
Learn Manx (free app)
Manx Songs and Rhymes (free Android app)
Manx Songs and Rhymes (free iTunes app)

Manx Radio
Adrian Cain’s Manx Language Podcast

Sean-Ghaeilge (Old Irish)

Sengoidelc: Old Irish for Beginners by David Stifter
Old Irish Workbook (Irish Studies) by Ernest Gordon Quin
A Grammar of Old Irish (Irish language: grammar) by Rudolf Thurneysen
A first Old Irish grammar and reader: including an introduction to Middle Irish by Kim McCone
Old Irish Verbs and Vocabulary by Antony Green

In Dúil Bélrai – gluais Sean-Ghaeilge
Electronic Dictionary of the Irish Language (eDIL)
Sengoídelc: Quotations from Early Irish Literature

Old Irish Online
Old Irish at Memrise