"Angular Harps Through the Ages, A Causal History" by Bo Lawergren. A scholarly, illustrated article about the angular harp 3000 B.C. to 1600 A.D
See also his article on angular harps in the summer issue (2011) of Early Music America.

Celtic Harp - From ancient times to the present.

Chromatic Harp

Early Gaelic Harp Info - the historical Gaelic harp tradition of Ireland and the Highlands and Islands of Scotland.

Early Welsh Music and Instruments - medieval and renaissance Welsh music and poetry with voice, crwth and lyre.

Early, Medieval, Celtic Harps

Gaelic Harps and Harpers in Ireland and Scotland

Hair Raising Harp History: Deborah Henson-Conant asks questions, Nancy Thym-Hochrein answers.

Harp History

Harp History Info -  a site by Ark van Campen in the Netherlands. It contains many, many drawings, images and captions.

Harp History and Culture - A listing of book titles.

The Harp: History, Care and Feeding of

The Harp in Wales

Historical Harps  - Includes illustrations of over 40 existing harps from at least three millennia

History of the Harp in Scotland

The kora (French: cora) -- the 21 string harp-lute played by Mandingo peoples throughout West Africa.

"Nicolas-Charles Bochsa: harpiste, compositeur, escroc (harpist, composer, crook)", new biography (in French) by Michel Faul.

Small Harp History Since 1800 - Evolution of the small harp design.

The Wire-Strung Harp - Excerpts from Rensch, Rimmer, and other researchers.

Wire-Strung Harp - Information from Cynthia Cathcart

Wikipedia: harp history, types, world harps.