Die Dafne (1627) to a libretto by Martin Opitz (which survives), and music by Heinrich Schütz (which is lost), is traditionally regarded as the first German opera, though it is generally considered a Singspiel.
History of the work
Opitz was already a friend of Schütz and in all wrote twelve German madrigal texts for him. In 1625 and 1626 Opitz visited the Dresden court, to work with Schütz on a Sing-Comoedie based on the model of Jacopo Peri's Dafne. Opitz rewrote the libretto after Rinuccini, translating it into Alexandrine verse, and his libretto was so highly regarded that it was later adapted back into Italian by later Italian librettists. Opitz and Schütz' were probably attracted by religious content of the work, rather than the purely pagan mythology of Dafne or Euridice. The electoral secretary to the Saxon Court, Johann Seusse also exerted influence on the project.
Modern scholarly reevaluation
Although long unquestioned as "the first German opera" the performance started no notable tradition in Germany, and Wolfram Steude (1991) made the controversial proposal that Dafne was in fact a spoken drama with inserted song and ballet numbers. Consequently recent publications such as the latest edition of the New Grove Dictionary of Opera are more cautious in attribution of the "first German opera" claim. 
Other Singspiels by Schütz
Two other large scale sung dramas by Schütz are also lost:
- Orpheus und Eurydike (Dresden, 1638) — a ballet based on the myth about Orpheus and Eurydice, with libretto by August Buchner.
- Paris und Helena five act Sing-Ballet to a libretto by David Schirmer. For the double wedding in Dresden of the brothers Maurice, Duke of Saxe-Zeitz and Christian I, Duke of Saxe-Merseburg.
- Origins of opera
- Seelewig (1644) of Sigmund Staden, first surviving German opera
- Pomone (opera) (1671) of Robert Cambert, first French opera (lost)
- Venus and Adonis (opera) (1683) John Blow, first true English-language opera.
- Isabella Van Elferen -Mystical Love in the German Baroque: Theology, Poetry, Music - 2009 -Page 31 "The Dresden Kapellmeister Heinrich Schütz was a friend of Martin Opitz, who wrote twelve German madrigal texts for him.26 In 1625 and 1626 Opitz visited Dresden, where he worked with Schütz on a “Sing-Comoedie” entitled Dafne (first ..."
- A Alms Adapting an adaptation: Martin Opitz's Dafne among the Italians 2012 em.oxfordjournals.org/content/early/2012/02/23/em.car119.full 23 Feb 2012 "The 1627 Opitz–Schütz Dafne was in a sense a paradigmatic work: it presented a case that German opera could develop a lasting presence by ..."
- Judith Popovich Aikin -A language for German opera: the development for forms and ... 2002 "Schutz's enthusiasm (and Opitz's) can be ascribed, according to Mayer, to the religious content of the work, which he thought should be much more attractive to both Germans than the pagan mythology of Dafne or Euridice."
- Schütz-Jahrbuch: Volume 30; Volume 30 Internationale Heinrich Schütz-Gesellschaft, 2008 "Eine erste Begegnung Seusses mit Opitz könnte im August 1626 in Dresden erfolgt sein, als Schütz und Opitz das gemeinsame Dafne-Projekt besprachen. Opitz weilte in jenem Sommer in diplomatischer Mission des Burggrafen von Dohna in ..."
- Bettina Varwig Histories of Heinrich Schütz - Page 94 2011 "In 1991, Wolfram Steude published his controversial proposal that Dafne amounted to nothing more than a piece of 'spoken theatre with inserted song and ballet numbers'.2 The latest edition of the New Grove Dictionary of Opera ..."
- "David Schirmer's Ballet von dem Paris und der Helena (1650): An Example of Early German Musical Drama". Retrieved 2008-06-10.
- "German Literature Companion: August Buchner". Retrieved 2008-06-10.