Here are the most valuable books and other resources I have found on Richard Wagner’s great opera cycle, The Ring of the Nibelung (composed of Rhinegold, Valkyrie, Siegfried, and Twilight of the Gods.) Most links are for more info at Amazon.com, an affiliate.
Recordings
Note: Every Ring lover has their favorite recordings. I’m no opera expert myself, but these are ones I’ve enjoyed.
Der Ring des Nibelungen, performed by The Metropolitan Opera, conducted by James Levine, Polydor/Deutsche Grammophon, 1988. The orchestral playing is majestic, achingly lovely. My favorite. The Metropolitan also produced a 1990 live video version—though I personally prefer to use my imagination.
Der Ring des Nibelungen, conducted by Georg Solti, London, 1964. A classic recording noted for its sense of drama and fine voices.
Translations
Wagner’s Ring of the Nibelung: A Companion, edited by Stewart Spencer and Barry Millington, Thames & Hudson, New York, 2000. Includes Spencer’s full translation of the operas—probably the best standalone version available—plus valuable background articles.
The Ring of the Nibelung, translated by Andrew Porter, Norton, New York, 1983. Another good translation, noted for staying within the meter of the original German.
Commentary
Wagner Without Fear: Learning to Love—and Even Enjoy—Opera’s Most Demanding Genius, by William Berger, Vintage, New York, 1998. This is probably the best introduction to Wagner and his operas for the musical layman. Includes plot synopses, interesting facts, shameless gossip, raging controversies, survival tactics, and a good deal of humor.
Wagner, by Barry Millington, Princeton University, 1992. A fine introduction to Wagner and his operas for those with musical training.
Enjoying Wagner’s Ring of the Nibelung, by Spreight Jenkins, HighBridge Audio, 1996. A 4.5‑hour guided tour of the Ring, on audiocassette. Helps you recognize the many “motifs” (themes) that the music is famously built on.
Sources
Note: Wagner’s overall story of the Ring of the Nibelung did not come from German tradition or from any other—it is his own invention. However, he constructed it skillfully from diverse elements of German and Norse legend and mythology, bending them to his own purposes.
The Nibelungenlied, translated by A. T. Hatto, Penguin, New York, 1969. The German saga of the hero Siegfried. This was a major source not for the entire Ring cycle—as is often thought—but for the fourth opera, Twilight of the Gods.
The Saga of the Volsungs: The Norse Epic of Sigurd the Dragon Slayer, translated by Jesse Byock, Penguin, 1990. This Icelandic version of the Siegfried story was Wagner’s most important source for the Ring cycle as a whole.
The Poetic Edda, translated by Carolyne Larrington, Oxford University Press, 1996. A thirteenth-century collection of Icelandic bardic poetry. This is one of the two major sources for what we know about Norse mythology, and was one of Wagner’s main sources for the Ring.
The Prose Edda, by Snorri Sturluson, translated by Jean I. Young, University of California Press, 1971. A thirteenth-century Icelandic treatise on bardic poetry. This is our other major source for Norse mythology, and was another of Wagner’s main sources.
Miscellaneous
The Early Germans, by Malcolm Todd, Blackwell, Oxford, 1992. A look at Germany in the time of the Ring.
Rackham’s Color Illustrations for Wagner’s “Ring”, by Arthur Rackham, Dover, New York, 1979. Sixty-four watercolor illustrations by a classic illustrator, first published in 1910-11 with Margaret Armour’s Ring translation. He certainly loved the Rhinemaidens. The color in these reproductions is washed out compared to the original, but they’re still beautiful.