An arrangement of Cwm Rhondda for a trio of Oboes & English Horn.

Cwm Rhondda, taken from the Welsh name for the Rhondda Valley, is a popular hymn tune written by John Hughes.

It is usually used in English as a setting for William Williams’ text Guide Me, O Thou Great Jehovah (or, in some traditions, Guide Me, O Thou Great Redeemer),originally Arglwydd, arwain trwy’r anialwch in Welsh. On account of a line in this English translation, the tune (and hymn) is often called Bread of Heaven.

In Welsh the tune is most commonly used as a setting for a hymn by Ann Griffiths, Wele’n sefyll rhwng y myrtwydd.

John Hughes wrote the first version of the tune, which he called "Rhondda", in 1905 for the Cymanfa Ganu (hymn festival) in Pontypridd, when the enthusiasm of the 1904–1905 Welsh Revival still remained. The present form was developed for the inauguration of the organ at Capel Rhondda, in Hopkinstown in the Rhondda valley, in 1907. Hughes himself played the organ at this performance, using the English translation of William Williams’s words because of the large number of English-speaking industrial workers who had immigrated to the area. The name was changed from "Rhondda" to "Cwm Rhondda" by Harry Evans, of Dowlais, to avoid confusion with another tune by M O Jones.

The hymn is usually pitched in A-flat major and has the 8.7.8.7.4.7 measure which is common in Welsh hymns. The third line repeats the first and the fourth line develops the second. The fifth line normally involves a repeat of the four-syllable text and the sixth reaches a climax on a dominant-seventh chord—emphasised by a rising arpeggio in the alto and bass parts. The final line continues the musical development of the second and fourth (and generally carries a repeat of the text of the sixth). On account of these vigorous characteristics, the tune was resisted for some time in both Welsh and English collections but has now become firmly established.