Evening Prayer (Anglican)
Many composers, especially Anglican church composers, wrote settings (music) for these two canticles (which choir members often called “Mag and Nunc”).  Such composers include Edward Bairstow, Herbert Brewer, Orlando Gibbons, Herbert Howells, Henry Purcell, Charles Stanford, Herbert Sumsion, Thomas Tallis, Thomas Weelkes, Samuel Wesley and many others.  Some of the composers wrote several settings.  This is why different settings are often identified by the key they are in, e.g. Stanford in G, Stanford in C etc.  Sometimes they can be identified by the cathedral for which they were written.  Herbert Howells, for example, wrote Mag and Nunc settings for several cathedrals and chapels.  These can be identified by calling them: Howells’ Gloucester Service, Collegium Regale (=King’s College, Cambridge) etc.