What is the Mixolydian mode?

Musical 'modes' are basically a set of tonalities deriving from a normal natural major scale. With C major, for example, it seems obvious that one should begin and end on C: C-D-E-F-G-A-B-C. But what if we used the same pitches while starting on the dominant? The new scale would be G-A-B-C-D-E-F-G. Of course, this can still be understood as C major; however, the emphasis now lies on G as a tonic. And yet this is not a natural G major scale, for it has a minor seventh (rather than a major seventh). This scale is called the Mixolydian scale, and pieces employing it can therefore be understood as being in the Mixolydian mode. The mode was quite popular among Romantic composers (see, for instance, the finale of Grieg's First Piano Concerto). Some more recent works in the Mixolydian mode include Lynyrd Skynyrd's 'Sweet Home Alabama' and 'Clocks' by Coldplay.