A great site with vocabulary lists, stories in Welsh and much more
clwb malu cacu

Dyfal Donc - Lessons 1-18
One of the best learning Welsh courses for beginners.
Dyfal Donc

The BBC Learn Welsh Site. Lots of resources for learners
BBC Learn Welsh

Interactive exercises for Welsh teachers and learners. Intended for school-age but fun for adults learners too
Sut (How)

The BBC Story of Welsh Site. History of the language and more
BBC Story of Welsh

The story of the poet and bard Hedd Wynn (Ellis Humphrey Evans)
Hedd Wynn

The Welsh Language Board Site
Bwrdd Yr Iaith

Find out how to turn your computer Welsh :-)
Cyfryfiadur Cymraeg

The BBC Welsh In The Workplace Site. Hear Welsh spoken and learn vocabulary. Jonesville is fun to visit.
BBC Welsh In the Workplace

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More links will be added soon.