[2] The book dates from the mid-13th century; its name comes from its association with the Priory of St. John the Evangelist and Teulyddog at Carmarthen, and is referred to as black due to the colour of its binding.

It is believed that the manuscript is first recorded when it came into the possession of Sir John Price of Brecon (1502?–1555), whose work was to search the monasteries dissolved by Henry VIII.

[3] The book contains a small group of triads about the horses of Welsh heroes, but is chiefly a collection of 9th–12th-century poetry falling into various categories: religious and secular subjects, and odes of praise and of mourning.

Of greater interest are the poems which draw on traditions relating to the Welsh heroes associated with the Hen Ogledd (Old North, i.e. Cumbria and the surrounding area), and especially those connected with the legend of Arthur and Myrddin, known in later non-Welsh tradition as Merlin, thus predating the descriptions of Merlin by Geoffrey of Monmouth.

[5] In March 2015, University of Cambridge Professor Paul Russell and Ph.D. student Myriah Williams reported that a variety of imaging techniques such as ultraviolet lamps and photo-editing software had revealed content that had been invisible under normal viewing conditions.